Precursor solutions and methods of using same

ABSTRACT

Superconductor precursor solutions are disclosed. The precursor solutions contain, for example, a salt of a rare earth metal, a salt of an alkaline earth metal and a salt of a transition metal. The precursor solutions can optionally include a Lewis base. The precursor solutions can be processed relatively quickly to provide a relatively thick and good quality intermediate of a rare earth metal-alkaline earth metal-transition metal oxide.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/694,400, filed Oct. 23, 2000, and entitled“Precursor Solutions and Methods of Using Same,” the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The invention relates to precursor solutions and methods of usingthe precursor solutions.

[0003] Multi-layer articles can be used in a variety of applications.For example, superconductors, including oxide superconductors, can beformed of multi-layer articles. Typically, such superconductors includea layer of superconductor material and a layer, commonly referred to asa substrate, that can enhance the mechanical strength of the multi-layerarticle.

[0004] Generally, in addition to enhancing the strength of themulti-layer superconductor, the substrate should exhibit certain otherproperties. For example, the substrate should have a low Curietemperature so that the substrate is not ferromagnetic at thesuperconductor's application temperature. Furthermore, chemical specieswithin the substrate should not be able to diffuse into the layer ofsuperconductor material, and the coefficient of thermal expansion of thesubstrate should be about the same as the superconductor material.Moreover, if the substrate is used for an oxide superconductor, thesubstrate material should be relatively resistant to oxidation.

[0005] For some materials, such as yttrium-barium-copper-oxide (YBCO),the ability of the material to provide high transport current in itssuperconducting state depends upon the crystallographic orientation ofthe material. For example, such a material can exhibit a relatively highcritical current density (Jc) when the surface of the material isbiaxially textured.

[0006] As used herein, “biaxially textured” refers to a surface forwhich the crystal grains are in close alignment with a direction in theplane of the surface. One type of biaxially textured surface is a cubetextured surface, in which the crystal grains are also in closealignment with a direction perpendicular to the surface. Examples ofcube textured surfaces include the (100)[001] and (100)[011] surfaces,and an example of a biaxially textured surface is the (113)[211]surface.

[0007] For certain multi-layer superconductors, the layer ofsuperconductor material is an epitaxial layer. As used herein,“epitaxial layer” refers to a layer of material whose crystallographicorientation is directly related to the crystallographic orientation ofthe surface of a layer of material onto which the epitaxial layer isdeposited. For example, for a multi-layer superconductor having anepitaxial layer of superconductor material deposited onto a substrate,the crystallographic orientation of the layer of superconductor materialis directly related to the crystallographic orientation of thesubstrate. Thus, in addition to the above-discussed properties of asubstrate, it can be also desirable for a substrate to have a biaxiallytextured surface or a cube textured surface.

[0008] Some substrates do not readily exhibit all the above-notedfeatures, so one or more intermediate layers, commonly referred to asbuffer layers, can be disposed between the substrate and thesuperconductor layer. The buffer layer(s) can be more resistant tooxidation than the substrate, and reduce the diffusion of chemicalspecies between the substrate and the superconductor layer. Moreover,the buffer layer(s) can have a coefficient of thermal expansion that iswell matched with the superconductor material.

[0009] Typically, a buffer layer is an epitaxial layer, so itscrystallographic orientation is directly related to the crystallographicorientation of the surface onto which the buffer layer is deposited. Forexample, in a multi-layer superconductor having a substrate, anepitaxial buffer layer and an epitaxial layer of superconductormaterial, the crystallographic orientation of the surface of the bufferlayer is directly related to the crystallographic orientation of thesurface of the substrate, and the crystallographic orientation of thelayer of superconductor material is directly related to thecrystallographic orientation of the surface of the buffer layer.Therefore, the superconducting properties exhibited by a multi-layersuperconductor having a buffer layer can depend upon thecrystallographic orientation of the buffer layer surface.

[0010] Certain superconductor precursor solutions can take a relativelylong period of time to form a superconductor intermediate (e.g., a metaloxyhalide intermediate). In some instances, trying to reduce this periodof time can result in the intermediate having a density of defects suchthat further treatment to form a superconductor material results in alayer of superconductor material with a relatively low critical currentdensity.

SUMMARY OF THE INVENTION

[0011] The invention relates in part to the realization that during theformation of certain rare earth-alkaline earth-transition metal oxides(e.g,. YBCO compounds such as YBa₂Cu₃O_(7−x)) defect formation can bereduced or prevented by selecting a precursor solution containing anappropriate salt of the rare earth metal, an appropriate salt of thealkaline earth metal, an appropriate salt of the transition metal, oneor more appropriate solvents, and optionally water. Such precursorsolutions can be used to form a relatively high quality (e.g., lowdefect density), relatively thick (e.g., at least about one micrometerthick) intermediate of the rare earth-alkaline earth-transition metaloxide (e.g., a metal oxyhalide intermediate) in a relatively shortperiod of time (e.g., less than about five hours). The intermediate canthen be further processed to form a rare earth-alkaline earth-transitionmetal oxide (e.g., an YBCO compound, such as YBa₂Cu₃O_(7−x)) having alow defect density and/or a relatively critical current density (e.g.,at least about 0.5×10⁶ Amperes per square centimeter).

[0012] An illustrative and nonlimiting list of solvents includes water,alcohols (e.g., methanol, 2-methoxyethanol, butanol, isopropanol),acetonitrile, tetrahydrofuran, 1-methyl-2-pyrrolidinone and pyridine.Combinations of two or more of these solvents can be used.

[0013] The constituents of the precursor solution should be selected sothat during processing of the precursor solution to form theintermediate of the rare earth-alkaline earth-transition metal oxide atleast one, and preferably substantially all, of the following parametersare met.

[0014] One parameter is that minimal alkaline earth carbonate (e.g.,BaCO₃) formation occurs when processing precursor solution to form theintermediate (e.g., metal oxyhalide). Preferably, the amount of alkalineearth carbonate formed is not detectable by X-ray diffraction. Withoutwishing to be bound by theory, it is believed that alkaline earthcarbonate formation can be undesirable because the alkaline earthcarbonate (e.g., BaCO₃) can be thermally stable at temperatures abovethe formation temperature of the formation temperature of the rareearth-alkaline earth-transition metal oxide (e.g., YBa₂Cu₃O_(7−x)),thereby reducing the amount of rare earth-alkaline earth-transitionmetal oxide formed. In certain embodiments, the alkaline earth metalsalts contained in the precursor solution are selected so that, ratherthan forming alkaline earth oxide(s) (e.g., BaO), they preferentiallyform alkaline earth compounds that undergo little if any conversion toalkaline earth carbonate (e.g., alkaline earth halide(s), such as BaF₂,BaCl₂, BaBr₂ and/or BaI₂). The alkaline earth compound (e.g., alkalineearth halide) should also be capable of being converted to appropriatealkaline earth oxide(s) (e.g., BaO) at a later time when the alkalineearth oxide(s) will quickly react with rare earth oxide(s) (e.g., Y₂O₃)and transition metal oxide(s) (e.g., CuO) to form the rare earthmetal-alkaline earth metal-transition metal oxide (e.g., an YBCOcompound, such as (YBa₂Cu₃O_(7−x))).

[0015] Another parameter is that minimal defect formation occurs duringformation of the rare earth-alkaline earth-transition metal oxideintermediate (e.g., metal oxyhalide intermediate). As used herein, a“defect” refers to a crack or a blister, such as a crack or blister thatis detectable by visual (or optical) inspection.

[0016] An additional parameter is that is the rare earth metal-alkalineearth metal-transition metal oxide intermediate has no compositionalphase segregations of a size that is more than about one tenth thethickness of the intermediate film. Further processing of such anintermediate can result in a rare earth metal-alkaline earthmetal-transition metal oxide that is substantially homogeneous (e.g.,YBa₂Cu₃O_(7−x) that is substantially 123 phase).

[0017] Another parameter is that, during conversion of the precursor tothe intermediate (e.g., metal oxyhalide), minimal cross-linking occursbetween discrete transition metal molecules (e.g., copper molecules).Without wishing to be bound by theory, it is believed that, whenprocessing the precursor solution to form the intermediate (e.g., metaloxyhalide), some transition metal salts can undergo chemical reactionsin which discrete copper molecules become cross-linked. It is believedthat such cross-linked molecules have a relatively high susceptibilityto defect formation. Without wishing to be bound by theory, it isbelieved that this cross-linking can occur when water coordinated in theoctahedral sites of the transition metal (e.g., copper) is displacedduring processing (e.g., at a temperature in the range of from about200° C. to about 220° C. for some transition metal salts), therebyopening bonding sites on the transition metal atom of one transitionmetal molecule to interact with atoms (e.g., oxygen or fluorine) ofanother transition metal molecule. In some embodiments, it is believedthat formation of such cross-linked discrete transition metal moleculescan be reduced by selecting a transition metal salt (e.g., copper salt)that sterically and/or chemically hinders the cross-linking duringprocessing (e.g., by using relatively large organic groups or relativelylarge atoms, such as chlorine, bromine or iodine, in the transitionmetal salt, or by using relatively electropositive atoms, such ashydrogen, in the transition metal salt).

[0018] Another parameter is that the rare earth metal salt should beselected such that during processing the salt is converted to rare earthmetal oxide(s) (e.g. Y₂O₃), as opposed to other compounds.

[0019] In one aspect, the invention features a method that includesdisposing a precursor solution onto a surface of a layer to form aprecursor film. The precursor film includes a salt of a rare earthmetal, a salt of an alkaline earth metal and a carboxylate salt of atransition metal (e.g., a propionate salt of a transition metal). Forexample, the transition metal salt can be Cu(O₂CC₂H₅)₂. The method alsoincludes treating the precursor film to form a layer of an intermediateof a rare earth metal-alkaline earth metal-transition metal oxide.

[0020] In another aspect, the invention features a method that includesdisposing a precursor solution onto a surface of a layer to form aprecursor film. The precursor film includes a salt of a rare earthmetal, a salt of an alkaline earth metal and a carboxylate salt ofcopper (e.g., CU(O₂CC₂H₅)₂). The method also includes treating theprecursor film to form a layer of an intermediate of a rare earthmetal-alkaline earth metal-transition metal oxide.

[0021] In a further aspect, the invention features a method thatincludes disposing a precursor solution onto a surface of a layer toform a precursor film. The precursor film includes a salt of a rareearth metal, a salt of an alkaline earth metal and a carboxylate salt ofa transition metal (e.g., a propionate salt of a transition metal). Forexample, the transition metal salt can be Cu(O₂CC₂H₅)₂. The method alsoincludes treating the precursor film to form a layer of an intermediateof a rare earth metal-alkaline earth metal-transition metal oxide.

[0022] In general, a precursor film can be formed by disposing aprecursor solution onto the surface of a layer of material, with orwithout further processing (e.g., the precursor film can be formed ofthe same chemical components as the precursor solution). For example, aprecursor film containing a salt of a rare earth metal, a salt of analkaline earth metal and a salt of a transition metal can be disposedonto the surface of a layer of material by, for example, dip coating,spin coating, slot coating or web coating. In some embodiments, themethod of disposing the precursor solution (e.g., spin coating) on thelayer of material can convert the precursor solution into a precursorfilm (e.g., by at least partially removing solvent(s) from the precursorsolution) without additional processing.

[0023] In another aspect, the invention features a composition thatincludes a salt of a rare earth metal, a salt of an alkaline earth metaland a carboxylate salt of copper (e.g., Cu(O₂CC₂H₅)₂).

[0024] In one aspect, the invention features a method that includesdisposing a precursor solution onto a surface of a layer to form aprecursor film. The precursor film includes a salt of a rare earthmetal, a salt of an alkaline earth metal, a salt of a transition metaland a Lewis base. The method also includes treating the precursor filmto form an intermediate of a rare earth metal-alkaline earthmetal-transition metal oxide.

[0025] In another aspect, the invention features a composition thatincludes a Lewis base, a salt of a rare earth metal, a salt of analkaline earth metal and a salt of a transition metal.

[0026] The superconductor intermediate can be, for example, partially orcompletely formed of one or more metal oxyhalide compounds.

[0027] The invention can be particularly advantageous when preparing asuperconductor in the form of an object having a relatively largesurface area, such as a tape or a wafer.

[0028] In some embodiments, the superconductor material is preferablyformed of YBCO (e.g., YBa₂Cu₃O_(7−x)).

[0029] The superconductor material can have a critical current of atleast about 200 Amperes per centimeter of width (e.g., at least about300 Amperes per centimeter of width, at least about 500 centimeters percentimeter of width).

[0030] Unless otherwise defined, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this invention belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice of the invention, suitable methods and materials aredescribed below. In case of conflict, the present specification,including definitions, will control. In addition, the materials,methods, and examples are illustrative only and not intended to belimiting.

[0031] Other features and advantages of the invention will be apparentfrom the description of the preferred embodiments, the figures and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a cross-sectional view of one embodiment of amulti-layer article;

[0033]FIG. 2 is a cross-sectional view of another embodiment of amulti-layer article;

[0034]FIG. 3 is a cross-sectional view of a further embodiment of amulti-layer article; and

[0035]FIG. 4 is an optical micrograph of a film of an intermediatematerial;

[0036]FIG. 5 is a θ-2θ X-ray diffraction scan of a film ofYBa₂Cu₃O_(7−x);

[0037]FIG. 6 is a θ-2θ X-ray diffraction scan of a film ofYBa₂Cu₃O_(7−x);

[0038]FIG. 7 is an optical micrograph of a film of an intermediatematerial;

[0039]FIG. 8 is an optical micrograph of a film of an intermediatematerial;

[0040]FIG. 9 is an optical micrograph of a film of an intermediatematerial;

[0041]FIG. 10 is an optical micrograph of a film of an intermediatematerial

[0042]FIG. 11 is a θ-2θ X-ray diffraction scan of a film ofYBa₂Cu₃O_(7−x);

[0043]FIG. 12 is a θ-2θ X-ray diffraction scan of a film ofYBa₂Cu₃O_(7−x); and

[0044]FIG. 13 is a θ-2θ X-ray diffraction scan of a film ofYBa₂Cu₃O_(7−x).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The invention relates to precursor solutions and methods of usingthe precursor solutions.

[0046] The precursor solutions contain a salt of a rare earth metal, asalt of an alkaline earth metal, a salt of a transition metal, and oneor more solvents. Optionally, the precursor solutions can contain water.In some embodiments, the precursor solutions can contain one or moreLewis bases.

[0047] The rare earth metal can be yttrium, lanthanum, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,cerium, praseodymium, neodymium, promethium, samarium or lutetium. Ingeneral, the rare earth metal salt can be any rare earth metal salt thatis soluble in the solvent(s) contained in the precursor solution andthat, when being processed to form an intermediate (e.g., a metaloxyhalide intermediate), forms rare earth oxide(s) (e.g., Y₂O₃). Suchsalts can have, for example, the formula M(O₂C—(CH₂)_(n)—CXX

X

)(O₂C—(CH₂)_(m)—CX

X

X

)(O₂C—(CH₂)_(p)—CX

X

X

) or more M(OR)₃. M is the rare earth metal. n, m and p are each atleast one but less than a number that renders the salt insoluble in thesolvent(s) (e.g., from one to ten). Each of X, X

, X

, X

, X

, X

,X

, X

and X

is H, F, Cl, Br or I. R is a carbon containing group, which can behalogenated (e.g., CH₂CF₃) or nonhalogenated. Examples of such saltsinclude nonhalogenated carboxylates, halogenated acetates (e.g.,trifluoroacetate, trichloroacetate, tribromoacetate, triiodoacetate),halogenated alkoxides, and nonhalogenated alkoxides. Examples of suchnonhalogenated carboxylates include nonhalogenated actetates (e.g.,M(O₂C—CH₃)₃).

[0048] Typically, the alkaline earth metal is barium, strontium orcalcium. Generally, the alkaline earth metal salt can be any alkalineearth metal salt that is soluble in the solvent(s) contained in theprecursor solution and that, when being processed to form anintermediate (e.g., a metal oxyhalide intermediate), forms an alkalineearth halide compound (e.g., BaF₂, BaCl₂, BaBr₂, BaI₂) prior to formingalkaline earth oxide(s) (e.g, BaO). Such salts can have, for example,the formula M

(O₂C—(CH₂)_(n)—CXX

X

)(O₂C—(CH₂)_(m)—CX

X

X

) or M

(OR)₂. M

is the alkaline earth metal. n and m are each at least one but less thana number that renders the salt insoluble in the solvent(s) (e.g., fromone to ten). Each of X, X

, X

, X

, X

and X

is H, F, Cl, B or, I. R can be a halogenated or nonhalogenated carboncontaining group. Examples of such salts include halogenated acetates(e.g., trifluoroacetate, trichloroacetate, tribromoacetate,triiodoacetate).

[0049] Generally, the transition metal is copper. The transition metalsalt should be soluble in the solvent(s) contained in the precursorsolution. Preferably, during conversion of the precursor to theintermediate (e.g., metal oxyhalide), minimal cross-linking occursbetween discrete transition metal molecules (e.g., copper molecules).Such transition metals salts can have, for example, the formula M

(CXX

X

-CO(CH)_(a)CO—CX

X

X

)(CX

X

X

-CO(CH)_(b)CO CX

X

X

), M

(O₂C—(CH₂)_(n)—CXX

X

) (O₂C—(CH₂)_(m)—CX

X

X

) or M

(OR)₂. M

is the transition metal. a and b are each at least one but less than anumber that renders the salt insoluble in the solvent(s) (e.g., from oneto five). Generally, n and m are each at least one but less than anumber that renders the salt insoluble in the solvent(s) (e.g., from oneto ten). Each of X, X

, X

, X

, X

, X

, X

, X

, X

, X

, X

, X

is H, F, Cl, Br or I. R is a carbon containing group, which can behalogenated (e.g., CH₂CF₃) or nonhalogenated. These salts include, forexample, nonhalogenated actetates (e.g., M

(O₂C—CH₃)₂), halogenated acetates, halogenated alkoxides, andnonhalogenated alkoxides. Examples of such salts include coppertrichloroacetate, copper tribromoacetate, copper triiodoacetate,Cu(CH₃COCHCOCF₃)₂, Cu(OOCC₇H₁₅)₂, Cu(CF₃COCHCOF₃)₂, Cu(CH₃COCHCOCH₃)₂,Cu(CH₃CH₂CO₂CHCOCH₃)₂, CuO(C₅H₆N)₂ and Cu₃O₃Ba₂(O—CH₂CF₃)₄. In certainembodiments, the transition metal salt is a carboxylate salt (e.g., anonhalogenated carboxylate salt), such as a propionate salt of thetransition metal (e.g., a nonhalogenated propionate salt of thetransition metal). An example of a nonhalogenated propionate salt of atransition metal is CU(O₂CC₂H₅)₂. In some embodiments, the transitionmetal salt is a simple salt, such as copper sulfate, copper nitrate,copper iodide and/or copper oxylate. In some embodiments, n and/or m canhave the value zero. In certain embodiments, a and/or b can have thevalue zero.

[0050] An illustrative and nonlimiting list of Lewis bases includesnitrogen-containing compounds, such as ammonia and amines. Examples ofamines include CH₃CN, C₅H₅N and R₁R₂R₃N. Each of R₁ R₂ R₃ areindependently H, an alkyl group (e.g., a straight chained alkyl group, abranched alkyl group, an aliphatic alkyl group, a non-aliphatic alkylgroup and/or a substituted alkyl group) or the like. Without wishing tobe bound by theory, it is believed that the presence of a Lewis base inthe precursor solution can reduce cross-linking of copper duringintermediate formation. It is believed that this is achieved because aLewis base can coordinate (e.g., selective coordinate) with copper ions,thereby reducing the ability of copper to cross-link.

[0051] In certain embodiments, the precursor solutions can have arelatively low total free acid concentration. In some embodiments, theprecursor solutions have a total free acid concentration of less thanabout 1×10⁻³ molar (e.g., less than about 1×10^(−≡)molar, about 1×10⁻⁷molar). Examples of free acids that can be contained in the precursorsolutions include trifluoroacetic acid, acetic acid, nitric acid,sulfuric acids, acids of iodides, acids of bromides and acids ofsulfates.

[0052] In some embodiments, such as when the precursor solutions containwater, the precursor solutions can have a relatively neutral pH. Forexample, the pH of the precursor solutions can be at least about 3(e.g., at least about 5, about 7).

[0053] The precursor solutions can have a relatively low water content.In certain embodiments, the precursor solutions have a water content ofless than 50 volume percent, more (e.g., less than about 35 volumepercent, less than 25 volume percent).

[0054] The amount of the transition metal, alkaline earth metal and rareearth metal can be selected so that the ratio of the molar amount ofeach of these elements (e.g, in the ionic state) in the precursorsolution is about 3:2:1.

[0055] In certain embodiments, the alkaline earth metal salt (e.g.,barium salt) is the predominant (e.g., exclusive) source of the halogenused to form the alkaline earth metal halide when processing theprecursor solution to form the intermediate (e.g., the metal oxyhalideintermediate). In other embodiments, such as when the rare earth metalsalt undergoes decomposition at the same time as the alkaline earthmetal salt, the rare earth salt can also supply halogen to the alkalineearth metal. In some embodiments, such as when the transition metal saltundergoes decomposition at the same time as the alkaline earth metalsalt, the transition metal salt can also supply halogen to the alkalineearth metal. In certain embodiments, when both the rare earth metal saltand the transition metal salt undergo decomposition at the same time asthe alkaline earth metal salt, the rare earth metal salt and thetransition metal can supply halogen to the alkaline earth metal.

[0056] In general, the precursor solutions can be prepared by combiningthe salts of the rare earth metal, the transition metal and the alkalineearth metal with the desired solvent(s) and optionally water and/or oneor more Lewis bases. In certain embodiments, the salts are combined sothat the mole ratio of the transition metal salt:alkaline earth metalsalt:rare earth metal salt in the precursor solution is about 3:2: 1.

[0057] Subsequent to formation of the precursor solution, the solutioncan be disposed on the surface of an underlying layer (e.g., bufferlayer, superconductor layer or substrate). Generally, the particularsolvent(s) used, as well as the amount of the solvent(s) and/or watercontained in the precursor solutions can be selected based upon thetechnique that will be used to dispose the precursor solution on thesurface of the underlying layer . For example, if the solution will bedip coated, spin coated or web coated onto the surface of the underlyingmaterial layer, one or more alcohols (e.g., methanol, 2-methoxyethanol,butanol and/or isopropanol) can be used, and the amount of solvent(s)can be selected so that the desired viscosity and solids content isachieved. In embodiments in which the precursor solution is to be webcoated on the underlying layer, it may be desirable for the precursorsolution to have a kinematic viscosity of from about one centiStoke toabout 10 centiStokes.

[0058] Subsequent to being disposed on the surface of the underlyinglayer, the solution is treated to form a layer of superconductormaterial. This treatment generally involves heating at appropriate ratesand in an appropriate gas environment so that during conversion of theprecursor solution to the intermediate (e.g., a metal oxyhalideintermediate), minimal alkaline earth carbonate (e.g., BaCO₃) forms andminimal cross-linking occurs between discrete transition metal molecules(e.g., copper molecules). The intermediate (e.g., metal oxyhalideintermediate) is then further heated to form the desired superconductormaterial. Certain methods of forming the intermediate and thesuperconductor material are described below.

[0059]FIG. 1 shows a multi-layer superconductor 10 according to oneembodiment of the invention and prepared using the above-describedmethods. Article 10 includes a substrate layer 12 with a surface 13 anda superconductor material layer 14 with a surface 15. Layer 14 isdisposed on surface 13.

[0060] Layer 12 can be formed of any material capable of supportinglayer 14. In embodiments in which article 10 is a multi-layersuperconductor, layer 12 can be formed of a substrate material. Examplesof substrate materials that can be used as layer 12 include for example,metals and/or alloys, such as nickel, silver, copper, zinc, aluminum,iron, chromium, vanadium, palladium, molybdenum and/or their alloys.

[0061] Surface 13 of layer 12 can also be prepared using vacuumprocesses, such as ion beam assisted deposition, inclined substratedeposition and other vacuum techniques known in the art to form abiaxially textured surface on, for example, a randomly orientedpolycrystalline surface.

[0062] In some embodiments, a buffer layer can be formed using ion beamassisted deposition (IBAD). In this technique, a buffer layer materialis evaporated using, for example, electron beam evaporation, sputteringdeposition, or pulsed laser deposition while an ion beam (e.g., an argonion beam) is directed at a smooth amorphous surface of a substrate ontowhich the evaporated buffer layer material is deposited.

[0063] For example, the buffer layer can be formed by ion beam assisteddeposition by evaporating a buffer layer material having a rock-saltlike structure (e.g., a material having a rock salt structure, such asan oxide, including MgO, or a nitride) onto a smooth, amorphous surface(e.g., a surface having a root mean square roughness of less than about100 Angstroms) of a substrate so that the buffer layer material has asurface with substantial alignment (e.g., about 13° or less), bothin-plane and out-of-plane.

[0064] The conditions used during deposition of the buffer layermaterial can include, for example, a substrate temperature of from about0° C. to about 400° C. (e.g., from about room temperature to about 400°C.), a deposition rate of from about 1.0 Angstrom per second to about4.4 Angstroms per second, an ion energy of from about 200 eV to about1200 eV, and/or an ion flux of from about 110 microamperes per squarecentimeter to about 120 microamperes per square centimeter.

[0065] In some embodiments, when using IBAD, the substrate is formed ofa material having a polycrystalline, non-amorphous base structure (e.g.,a metal alloy, such as a nickel alloy) with a smooth amorphous surfaceformed of a different material (e.g., Si₃N₄).

[0066] In certain embodiments, a plurality of buffer layers can bedeposited by epitaxial growth on an original IBAD surface. Each bufferlayer can have substantial alignment (e.g., about 13° or less), bothin-plane and out-of-plane.

[0067] These methods are described in PCT Publication No. WO 99/25908,published on May 27, 1999, and entitled “Thin Films Having ARock-Salt-Like Structure Deposited on Amorphous Surfaces,” which ishereby incorporated by reference.

[0068] In other embodiments, the substrate can be formed of alloyshaving one or more surfaces that are biaxially textured (e.g.,(113)[211]) or cube textured (e.g., (100)[001] or (100)[011]). Thealloys can have a relatively low Curie temperature (e.g., at most about80K, at most about 40K, or at most about 20K).

[0069] In some of these embodiments, the substrate is a binary alloythat contains two of the following metals: copper, nickel, chromium,vanadium, aluminum, silver, iron, palladium, molybdenum, gold and zinc.For example, a binary alloy can be formed of nickel and chromium (e.g.,nickel and at most 20 atomic percent chromium, nickel and from aboutfive to about 18 atomic percent chromium, or nickel and from about 10 toabout 15 atomic percent chromium). As another example, a binary alloycan be formed of nickel and copper (e.g., copper and from about five toabout 45 atomic percent nickel, copper and from about 10 to about 40atomic percent nickel, or copper and from about 25 to about 35 atomicpercent nickel). A binary alloy can further include relatively smallamounts of impurities (e.g., less than about 0.1 atomic percent ofimpurities, less than about 0.01 atomic percent of impurities, or lessthan about 0.005 atomic percent of impurities).

[0070] In certain of these embodiments, the substrate contains more thantwo metals (e.g., a ternary alloy or a quarternary alloy). In theseembodiments the alloy can contain one or more oxide formers (e.g., Mg,Al, Ti, Cr, Ga, Ge, Zr, Hf, Y, Si, Pr, Eu, Gd, Tb, Dy, Ho, Lu, Th, Er,Tm, Be, Ce, Nd, Sm, Yb and/or La, with Al being the preferred oxideformer), as well as two of the following metals: copper, nickel,chromium, vanadium, aluminum, silver, iron, palladium, molybdenum, goldand zinc. The alloys can contain at least about 0.5 atomic percent oxideformer (e.g., at least about one atomic percent oxide former, or atleast about two atomic percent oxide former) and at most about 25 atomicpercent oxide former (e.g., at most about 10 atomic percent oxideformer, or at most about four atomic percent oxide former). For example,the alloy can include an oxide former (e.g., at least about 0.5aluminum), from about 25 atomic percent to about 55 atomic percentnickel (e.g., from about 35 atomic percent to about 55 atomic percentnickel, or from about 40 atomic percent to about 55 atomic percentnickel) with the balance being copper. As another example, the alloy caninclude an oxide former (e.g., at least about 0.5 atomic aluminum), fromabout five atomic percent to about 20 atomic percent chromium (e.g.,from about 10 atomic percent to about 18 atomic percent chromium, orfrom about 10 atomic percent to about 15 atomic percent chromium) withthe balance being nickel. The alloys can include relatively smallamounts of additional metals (e.g., less than about 0.1 atomic percentof additional metals, less than about 0.01 atomic percent of additionalmetals, or less than about 0.005 atomic percent of additional metals).

[0071] A substrate formed of an alloy can be produced by, for example,combining the constituents in powder form, melting and cooling or, forexample, by diffusing the powder constituents together in solid state.The alloy can then be formed by deformation texturing (e.g, annealingand rolling, swaging, extrusion and/or drawing) to form a texturedsurface (e.g., biaxially textured or cube textured). Alternatively, thealloy constituents can be stacked in a jelly roll configuration, andthen deformation textured. In some embodiments, a material with arelatively low coefficient of thermal expansion (e.g, Nb, Mo, Ta, V, Cr,Zr, Pd, Sb, NbTi, an intermetallic such as NiAl or Ni₃Al, or mixturesthereof) can be formed into a rod and embedded into the alloy prior todeformation texturing.

[0072] These methods are described PCT Publication No. WO 00/58530,published on Oct. 5, 2000, entitled “Alloy Materials;” PCT PublicationNo. WO 00/58044, published on Oct. 5, 2000, entitled “Alloy Materials;”PCT Publication No. WO 99/17307, published on Apr. 8, 1999, and entitled“Substrates with Improved Oxidation Resistance;” and PCT Publication No.WO 99/16941, published on Apr. 8, 1999, and entitled “Substrates forSuperconductors,” all of which are hereby incorporated by reference.

[0073] In some embodiments, stable oxide formation can be mitigateduntil a first epitaxial (for example, buffer) layer is formed on thebiaxially textured alloy surface, using an intermediate layer disposedon the surface of the substrate. Intermediate layers suitable for use inthe present invention include those epitaxial metal or alloy layers thatdo not form surface oxides when exposed to conditions as established byP_(O2) and temperature required for the initial growth of epitaxialbuffer layer films. In addition, the buffer layer acts as a barrier toprevent substrate element(s) from migrating to the surface of theintermediate layer and forming oxides during the initial growth of theepitaxial layer. Absent such an intermediate layer, one or more elementsin the substrate would be expected to form thermodynamically stableoxide(s) at the substrate surface which could significantly impede thedeposition of epitaxial layers due to, for example, lack of texture inthis oxide layer.

[0074] In some of these embodiments, the intermediate layer is transientin nature. “Transient,” as used herein, refers to an intermediate layerthat is wholly or partly incorporated into or with the biaxiallytextured substrate following the initial nucleation and growth of theepitaxial film. Even under these circumstances, the intermediate layerand biaxially textured substrate remain distinct until the epitaxialnature of the deposited film has been established. The use of transientintermediate layers may be preferred when the intermediate layerpossesses some undesirable property, for example, the intermediate layeris magnetic, such as nickel.

[0075] Exemplary intermediate metal layers include nickel, gold, silver,palladium, and alloys thereof. Additional metals or alloys may includealloys of nickel and/or copper. Epitaxial films or layers deposited onan intermediate layer can include metal oxides, chalcogenides, halides,and nitrides. In some embodiments, the intermediate metal layer does notoxidize under epitaxial film deposition conditions.

[0076] Care should be taken that the deposited intermediate layer is notcompletely incorporated into or does not completely diffuse into thesubstrate before nucleation and growth of the initial buffer layerstructure causes the epitaxial layer to be established. This means thatafter selecting the metal (or alloy) for proper attributes such asdiffusion constant in the substrate alloy, thermodynamic stabilityagainst oxidation under practical epitaxial buffer layer growthconditions and lattice matching with the epitaxial layer, the thicknessof the deposited metal layer has to be adapted to the epitaxial layerdeposition conditions, in particular to temperature.

[0077] Deposition of the intermediate metal layer can be done in avacuum process such as evaporation or sputtering, or by electrochemicalmeans such as electroplating (with or without electrodes). Thesedeposited intermediate metal layers may or may not be epitaxial afterdeposition (depending on substrate temperature during deposition), butepitaxial orientation can subsequently be obtained during apost-deposition heat treatment.

[0078] In certain embodiments, substrate 12 can be in the form of anobject having a relatively large surface area (e.g., a tape or a wafer).In these embodiments, substrate 12 is preferably formed of a relativelyflexible material (e.g., deformation textured nickel or a deformationtextured nickel alloy).

[0079] Preferably, surface 13 of layer 12 has a relatively well definedcrystallographic orientation. For example, surface 13 can be a biaxiallytextured surface (e.g., a (113)[211] surface) or a cube textured surface(e.g., a (100)[011] surface or a (100)[001] surface). Preferably, thepeaks in an X-ray diffraction pole figure of surface 13 have a FWHM ofless than about 20° (e.g., less than about 15°, less than about 10°, orfrom about 5° to about 10°).

[0080] Layer 14 can be prepared using one or more of a variety oftechniques.

[0081] Generally, layer 14 is prepared using the above-describedsuperconductor precursor solution. The precursor solution is applied toa surface (e.g., a buffer layer surface), such as by spin coating orother techniques known to those skilled in the art, and subsequentlyheated. The precursor is first converted to a superconductorintermediate (e.g., a metal oxylhalide intermediate) in a relativelyshort period of time (e.g,. less than about five hours, less than abouttwo hours, less than about an hour, less than about 30 minutes, lessthan about 10 minutes). The superconductor intermediate can berelatively thick (e.g., more than about one micrometer thick, more thanabout two micrometers thick, more than about three micrometers thick,more than about four micrometers thick, more than about five micrometersthick, more than about six micrometers thick, more than about sevenmicrometers thick, more than about eight micrometers thick, more thanabout nine micrometers thick, more than about 10 micrometers thick). Thesuperconductor intermediate can have a relatively low defect density.For example, the superconductor intermediate can be substantially freeof any defect having a maximum dimension greater than about 200micrometers and the defects can form less than about 20 percent of anyvolume element of the superconductor intermediate defined by aprojection of one square centimeter of the surface of the superconductorintermediate (e.g., less than about 10 percent of any volume element ofthe precursor intermediate defined by a projection of one squarecentimeter of the surface of the superconductor intermediate, less thanabout five percent of any volume element of the composition defined by aprojection of one square centimeter of the surface of the superconductorintermediate).

[0082] A volume element of a layer of material defined by the projectionof a given area of a surface of the layer of material corresponds to thevolume of the layer of material whose edges are perpendicular to thegiven area of the surface of the layer of material.

[0083] The precursors can be processed using a variety of reactionconditions, including gas environment and temperature. Generally, theconditions selected are such that the precursor solution is converted ina relatively short period of time (e.g, less than about five hours, lessthan about three hours, less than about two hours, less than about onehour, less than about 30 minutes, less than about 10 minutes) to anintermediate (e.g., a metal oxyhalide intermediate) having a low defectdensity.

[0084] In certain embodiments, when forming an intermediate film (e.g.,metal oxyhalide film) having a thickness of at least about onemicrometer (e.g., at least about two micrometers, at least about threemicrometers, at least about four micrometers, at least about fivemicrometers, at least about six micrometers, at least about sevenmicrometers, at least about eight micrometers, at least about ninemicrometers, at least about 10 micrometers), the temperature can beramped from about 200° C. to about 220° C. at a rate of at least about0.5° C. per minute (e.g., at least about 1° C. per minute, at leastabout 2° C. per minute, at least about 5° C. per minute, at least about10° C. per minute, at least about 15° C. per minute, at least about 20°C. per minute).

[0085] In some embodiments, the precursor solution can be converted toan intermediate (e.g., a metal oxyhalide intermediate) having athickness of at least about one micrometer (e.g., at least about twomicrometers, at least about three micrometers, at least about fourmicrometers, at least about five micrometers, at least about sixmicrometers, at least about seven micrometers, at least about eightmicrometers, at least about nine micrometers, at least about 10micrometers) in less than about five hours (e.g., in less than about twohours, in less than about one hour, in less than about 30 minutes, inless than about 10 minutes). Defects contained within the film of theintermediate can form less than about 20 percent (e.g., less than about10 percent, less than about five percent, less than about one percent)of any volume element of the intermediate defined by a projection of onesquare centimeter of the surface of the intermediate, and theintermediate is free of any defect having a maximum dimension greaterthan about 200 micrometers (e.g., free of any defect having a maximumdimension greater than about 100 micrometers, free of any defect havinga maximum dimension greater than about 50 micrometers).

[0086] In some embodiments, when forming an intermediate film (e.g.,metal oxyhalide film) having a thickness less than about one micrometer,the temperature can be ramped from about 200° C. to about 220° C. at arate of at least about 1° C. per minute (e.g., at least about 5° C. perminute, at least about 10° C. per minute, at least about 15° C. perminute, at least about 20° C. per minute).

[0087] In some embodiments, the precursor solution can be converted toan intermediate (e.g., a metal oxyhalide intermediate) having athickness of less than about one micrometer in less than about fivehours (e.g., in less than about two hours, in less than about one hour,in less than about 30 minutes, in less than about 10 minutes). Defectscontained within the film of the intermediate can form less than about20 percent (e.g., less than about 10 percent, less than about fivepercent, less than about one percent) of any volume element of theintermediate defined by a projection of one square centimeter of thesurface of the intermediate, and the intermediate is free of any defecthaving a maximum dimension greater than about 200 micrometers (e.g.,free of any defect having a maximum dimension greater than about 100micrometers, free of any defect having a maximum dimension greater thanabout 50 micrometers).

[0088] In some embodiments, the precursor solution can be placed in apre-heated furnace at an appropriate temperature (e.g., at least about300° C., from about 300° C. to about 400° C., about 350° C.) for anappropriate period of time (e.g., from about 10 minutes to about fivehours, from about 10 minutes to about two hours, from about 10 minutesto about one hour, about 30 minutes) to form an intermediate (e.g., ametal oxyhalide intermediate). The intermediate can be relatively thick(e.g., at least about one micrometer, at least about two micrometers, atleast about three micrometers, at least about four micrometers, at leastabout five micrometers, at least about six micrometers, at least aboutseven micrometers, at least about eight micrometers, at least about ninemicrometers, at least about 10 micrometers). The intermediate can have arelatively low defect density. For example, defects contained within thefilm of the intermediate can form less than about 20 percent (e.g., lessthan about 10 percent, less than about five percent, less than about onepercent) of any volume element of the intermediate defined by aprojection of one square centimeter of the surface of the intermediate,and the intermediate is free of any defect having a maximum dimensiongreater than about 200 micrometers (e.g., free of any defect having amaximum dimension greater than about 100 micrometers, free of any defecthaving a maximum dimension greater than about 50 micrometers).

[0089] Generally, these methods are performed in a gas environmentcontaining sufficient oxygen so that organic molecules formed areremoved in the form of oxidized hydrocarbons. In some embodiments, thegas environment used while heating the precursor solution can be inaccordance with the following.

[0090] In certain of these embodiments, the solution is first heated inmoist oxygen (e.g., having a dew point in the range of from about 20° C.to about 75° C.) to a temperature in the range of from about 300° C. toabout 500° C. The coating is then heated for about one hour to atemperature of less than about 860° C. (e.g., less than about 810° C.)in a moist nitrogen-oxygen gas mixture (e.g., having a compositionincluding from about 0.5% to about 5% oxygen). Optionally, the coatingcan be further heated to a temperature of from about 860° C. to about950° C. for from about five to about 25 minutes. The coating issubsequently heated to a temperature of from about 400° C. to about 500°C. for at least about eight hours at in dry oxygen. The coating can thenbe cooled to room temperature in dry oxygen. These methods are describedin U.S. Pat. No. 5,231,074, issued on Jul. 27, 1993, and entitled“Preparation of Highly Textured Oxide Superconducting Films from MODPrecursor Solutions,” which is hereby incorporated by reference.

[0091] In alternate embodiments, the precursor solution is heated froman initial temperature (e.g., room temperature) to a temperature of fromabout 190° C. to about 215° C. (e.g., about 210° C.) in a water vaporpressure of from about 5 Torr to about 50 Torr water vapor (e.g., fromabout 5 Torr to about 30 Torr water vapor, or from about 10 Torr toabout 25 Torr water vapor). The nominal partial pressure of oxygen canbe, for example, from about 0.1 Torr to about 760 Torr. In theseembodiments, heating is then continued to a temperature of from about220° C. to about 290° C. (e.g., about 220° C.) in a water vapor pressureof from about 5 Torr to about 50 Torr water vapor (e.g., from about 5Torr to about 30 Torr water vapor, or from about 10 Torr to about 25Torr water vapor). The nominal partial pressure of oxygen can be, forexample, from about 0.1 Torr to about 760 Torr. This is followed byheating to about 400° C. at a rate of at least about 2° C. per minute(e.g., at least about 3° C. per minute, or at least about 5° C. perminute) in a water vapor pressure of from about 5 Torr to about 50 Torrwater vapor (e.g., from about 5 Torr to about 30 Torr water vapor, orfrom about 10 Torr to about 25 Torr water vapor) to form an intermediateof the superconductor material (e.g., a metal oxyfluoride intermediate).The nominal partial pressure of oxygen can be, for example, from about0.1 Torr to about 760 Torr. These methods are described in commonlyowned U.S. Provisional Patent Application Ser. No. 60/166,145, filed onNov. 18, 1999, and entitled “Methods and Compositions for Making aMulti-Layer Article,” and commonly owned U.S. patent application Ser.No. 09/615,991, filed Jul. 14, 2000, and entitled “Methods andCompositions for Making a Multi-layer Article,” both of which are herebyincorporated by reference.

[0092] In other embodiments, heating the precursor solution includes oneor more steps in which the temperature is held substantially constant(e.g., constant within about 10° C., within about 5° C., within about 2°C., within about 1° C.) for a relatively long period of time (e.g., morethan about one minute, more than about five minutes, more than about 30minutes, more than about an hour, more than about two hours, more thanabout four hours) after a first temperature ramp to a temperaturegreater than about room temperature. In these embodiments, heating theprecursor solution can involve using more than one gas environment(e.g., a gas environment having a relatively high water vapor pressureand a gas environment having a relatively low water vapor pressure)while maintaining the temperature substantially constant (e.g., constantwithin about 10° C., within about 5° C., within about 2° C., withinabout 1° C.) for a relatively long period of time (e.g., more than aboutone minute, more than about five minutes, more than about 30 minutes,more than about an hour, more than about two hours, more than about fourhours). As an example, in a high water vapor pressure environment, thewater vapor pressure can be from about 5 Torr to about 40 Torr (e.g.,from about 25 Torr to about 38 Torr, such as about 32 Torr). A low watervapor pressure environment can have a water vapor pressure of less thanabout 1 Torr (e.g., less than about 0.1 Torr, less than about 10milliTorr, about five milliTorr). These methods are described incommonly owned U.S. patent application Ser. No. 09/618,811, filed Jul.14, 2000, and entitled “Methods of Making A Superconductor,” which ishereby incorporated by reference.

[0093] In certain embodiments, heating the precursor solution caninclude putting the coated sample in a pre-heated furnace (e.g., at atemperature of at least about 100° C., at least about 150° C., at leastabout 200° C., at most about 300° C., at most about 250° C., about 200°C.). The gas environment in the furnace can have, for example, a totalgas pressure of about 760 Torr, a predetermined partial pressure ofwater vapor (e.g. at least about 10 Torr, at least about 15 Torr, atmost about 25 Torr, at most about 20 Torr, about 17 Torr) with thebalance being molecular oxygen. After the coated sample reaches thefurnace temperature, the furnace temperature can be increased (e.g., toat least about 225° C., to at least about 240° C., to at most about 275°C., to at most about 260° C., about 250° C.) at a predeterminedtemperature ramp rate (e.g., at least about 0.5° C. per minute, at leastabout 0.75° C. per minute, at most about 2° C. per minute, at most about1.5° C. per minute, about 1° C. per minute). This step can be performedwith the same nominal gas environment used in the first heating step.The temperature of the furnace can then be further increased (e.g., toat least about 350° C., to at least about 375° C., to at most about 450°C., to at most about 425° C., about 450° C.) at a predeterminedtemperature ramp rate (e.g., at least about 5° C. per minute, at leastabout 8° C. per minute, at most about 20° C. per minute, at most about12° C. per minute, about 10° C. per minute). This step can be performedwith the same nominal gas environment used in the first heating step.

[0094] In some embodiments, preparation of a superconductor material caninvolve slot coating the precursor solution (e.g., onto a tape, such asa tape formed of a textured nickel tape having sequentially disposedthereon epitaxial buffer and/or cap layers, such as Gd₂O₃, YSZ andCeO₂). The coated precursor film can deposited in an atmospherecontaining H₂O (e.g., from about 5 torr H₂O to about 15 torr H₂O, fromabout 9 torr H₂O to about 13 torr H₂O, about 11 torr H₂O) The balance ofthe atmosphere can be an inert gas (e.g., nitrogen). The total pressureduring film deposition can be, for example, about 760 torr. Theprecursor film can be decomposed, for example, by transporting thecoated tape through a tube furnace (e.g., a tube furnace having adiameter of about 2.5 inches) having a temperature gradient. Therespective temperatures and gas atmospheres of the gradients in thefurnace, as well as the transport rate of the sample through eachgradient, can be selected so that the processing of the film issubstantially the same as according to the above-noted methods.

[0095] The foregoing treatments of a precursor solution can result in ametal oxyhalide intermediate. Preferably, the metal oxyhalideintermediate has a relatively low defect density. The metal oxyhalideintermediate can be further heated to form the desired superconductorlayer. Typically, this step is performed by heating to a temperature offrom about 700° C. to about 825° C. During this step, the nominal gasenvironment typically can contain from about 0.1 Torr to about 50 Torroxygen and from about 0.1 Torr to about 150 Torr (e.g., about 12 Torr)of water vapor with the balance being nitrogen and/or argon.

[0096] Alternatively, the intermediate is then heated for about one hourto a temperature of less than about 860° C. (e.g., less than about 810°C.) in a moist reducing nitrogen-oxygen gas mixture (e.g., having acomposition including from about 0.5% to about 5% oxygen). Optionally,the coating can be further heated to a temperature of from about 860° C.to about 950° C. for from about five to about 25 minutes. The coating issubsequently heated to a temperature of from about 400° C. to about 500°C. for at least about eight hours in dry oxygen. The coating can then becooled to room temperature in static dry oxygen. This approach isdescribed in U.S. Pat. No. 5,231,074.

[0097] In other embodiments, the metal oxyhalide is converted into anoxide superconductor at a rate of conversion selected by adjustingtemperature, vapor pressure of gaseous water or both. For example, themetal oxyhalide can be converted in a processing gas having a moisturecontent of less than 100% relative humidity (e.g., less than about 95%relative humidity, less than about 50% relative humidity, or less thanabout 3% relative humidity) at 25° C. to form some oxide superconductor,then completing the conversion using a processing gas having a highermoisture content (e.g., from about 95% relative humidity to about 100%relative humidity at 25° C.). The temperature for converting the metaloxyhalide can be in the range of from about 700° C. to about 900° C.(e.g., from about 700° C. to about 835° C.). The processing gas cancontain from about 1 volume percent oxygen gas to about 10 volumepercent oxygen gas.

[0098] These methods are described in PCT Publication No. WO 98/58415,published on Dec. 23, 1998, and entitled “Controlled Conversion of MetalOxyfluorides into Superconducting Oxides,” which is hereby incorporatedby reference.

[0099] In particular embodiments, methods of treating the solution canbe employed to minimize the formation of undesirable a-axis orientedoxide layer grains, by inhibiting the formation of the oxide layer untilthe required reaction conditions are attained.

[0100] Conventional processes developed for decomposition and reactionof fluoride-containing precursors use a constant, and low, non-turbulentflow of process gas that is introduced into the decomposition furnace inan orientation that is parallel to the film surface, resulting in astable boundary layer at the film/gas interface. In the apparatus typestypically used for oxide layer precursor decomposition and reaction, thediffusion of gaseous reactants and products through this gas/filmboundary layer appears to control the overall reaction rates. In thin,small area films (for example, less than about 0.4 micrometers thick andless than about a square centimeter), the diffusion of H₂O into the filmand the diffusion of HF out of the film occur at rates such that theformation of the YBa₂Cu₃O_(7−x) phase does not begin at any significantrate until the sample reaches the processing temperature. However, asthe film thickness or area increases, the rates of gaseous diffusioninto and out of the film decrease, all other parameters being equal.This results in longer reaction times and/or incomplete formation of theYBa₂Cu₃O_(7−x) phase, resulting in reduced crystallographic texture,lower density, and reduced critical current density. Thus, the overallrate of YBa₂Cu₃O_(7−x) phase formation is determined, to a significantextent, by the diffusion of gases through the boundary layer at the filmsurface.

[0101] One approach to eliminating these boundary layers is to produce aturbulent flow at the film surface. Under such conditions, the local gascomposition at the interface is maintained essentially the same as inthe bulk gas (that is, the pH₂O is constant, and the pHF isapproximately zero). Thus, the concentration of the gaseousproducts/reactants in the film is not controlled by the diffusionthrough the gas/film surface boundary layer condition, but rather bydiffusion through the film. In order to minimize the nucleation ofa-axis YBa₂Cu₃O_(7−x) oriented grains on a substrate surface, theformation of the YBa₂Cu₃O_(7−x) phase is inhibited until desired processconditions are reached. For example, the formation of the YBa₂Cu₃O_(7−x)phase can be inhibited until desired process temperature is reached.

[0102] In one embodiment, a combination of: 1) low (non-turbulent)process gas flow, so that a stable boundary layer is established at thefilm/gas interface, during the ramp to temperature, and 2) high(turbulent) process gas flow, so that the boundary layer is disrupted atthe film/gas interface, is employed. For example, in a three inch tubefurnace, the flow can be from about 0.5 to about 2.0 L/min during thetemperature ramp from ambient temperature to the desired processtemperature. Thereafter, the flow can be increased to a value of fromabout 4 to about 15 L/min during the time at which the film is beingprocessed. Thus, the rate of formation of YBa₂Cu₃O_(7−x) and epitaxialtexture formation can be increased at high temperature, while minimizingthe amount of unwanted a-axis nucleation and growth at low temperatureduring ramp up. According to these processes, a-axis nucleated grainsare desirably present in an amount of less than about 1%, as determinedby scanning electron microscopy.

[0103] More details are provided in commonly owned U.S. patentapplication Ser. No. 09/616,566, filed on Jul. 14, 2000, and entitled“Control of Oxide Layer Reaction Rates,” which is hereby incorporated byreference.

[0104] In preferred embodiments, layer 14 has a relatively high criticalcurrent density (e.g., at least about 0.5×10⁶ Amperes per squarecentimeter). Preferably, layer 14 has a critical current density of atleast about 0.5×10⁶ Amperes per square centimeter, more preferably atleast about 1×10⁶ Amperes per square centimeter, and most preferably atleast about 2×10⁶ Amperes per square centimeter, as determined bytransport measurement at 77K in self field (i.e., no applied field)using a 1 micro Volt per centimeter criterion.

[0105] In certain embodiments, layer 14 can provide a relatively highcritical current, as measured in unites of Amperes per unit width. As anexample, the critical current can be expressed in units of Amperes percentimeter width. Of course, layer 14 need not be one centimeter wide.Rather, this value can be used for convenience to normalize the currentto width ratio value for materials having different widths. As anexample, a sample that has a current of 100 Amperes and is 0.5centimeter wide would have a critical current of 200 Amperes percentimeter width. A sample that provides a current of 200 Amperes and isone centimeter wide would also has a critical current of 200 Amperes percentimeter width. In preferred embodiments, layer 14 has a criticalcurrent of at least about 200 Amperes per centimeter of width (e.g., atleast about 300 Amperes per centimeter of width, at least about 500centimeters per centimeter of width).

[0106] In preferred embodiments, layer 14 is well-ordered (e.g.,biaxially textured or cube textured). Layer 14 can be at least about onemicrometer thick (e.g., at least about two micrometers thick, at leastabout three micrometers thick, at least about four micrometers thick, atleast about five micrometers thick).

[0107]FIG. 2 shows an embodiment of an article 20 that can be formed bythe methods of the invention. Article 20 includes layers 12 and 14.Article 20 also includes a layer 16 disposed between layers 12 and 14such that layer 16 is disposed on surface 13 and layer 14 is disposed ona surface 17 of layer 16.

[0108] Layer 16 can be formed of any material capable of supportinglayer 14. For example, layer 16 can be formed of one or more layers ofbuffer layer material. Examples of buffer layer materials include metalsand metal oxides, such as silver, nickel, TbO_(x), GaO_(x), CeO₂,yttria-stabilized zirconia (YSZ), Y₂O₃, LaAlO₃, SrTiO₃, Gd₂O₃, LaNiO₃,LaCuO₃, SrRuO₃, NdGaO₃, NdAlO₃ and/or some nitrides as known to thoseskilled in the art. A buffer material can be prepared using solutionphase techniques, including metalorganic deposition, such as disclosedin, for example, S.S. Shoup et al., J. Am. Cer. Soc., vol. 81, 3019; D.Beach et al., Mat. Res. Soc. Symp. Proc., vol. 495, 263 (1988); M.Paranthaman et al., Superconductor Sci. Tech., vol. 12, 319 (1999); D.J. Lee et al., Japanese J. Appl. Phys., vol. 38, L178 (1999) and M. W.Rupich et al., I.E.E.E. Trans. on Appl. Supercon. vol. 9, 1527.

[0109] In certain embodiments, solution coating processes can be usedfor deposition of one or a combination of any of the oxide layers ontextured substrates; however, they can be particularly applicable fordeposition of the initial (seed) layer on a textured metal substrate.The role of the seed layer is to provide 1) protection of the substratefrom oxidation during deposition of the next oxide layer when carriedout in an oxidizing atmosphere relative to the substrate (for example,magnetron sputter deposition of yttria-stabilized zirconia from an oxidetarget); and 2) an epitaxial template for growth of subsequent oxidelayers. In order to meet these requirements, the seed layer should growepitaxially over the entire surface of the metal substrate and be freeof any contaminants that may interfere with the deposition of subsequentepitaxial oxide layers.

[0110] The formation of oxide buffer layers can be carried out so as topromote wetting of an underlying substrate layer. Additionally, inparticular embodiments, the formation of metal oxide layers can becarried out using metal alkoxide precursors (for example, “sol gel”precursors), in which the level of carbon contamination can be greatlyreduced over other known processes using metal alkoxide precursors.

[0111] If the substrate underlying an oxide layer is insufficientlycovered by a precursor solution used to make the oxide layer, then theoxide layer will not provide the desired protection of the substratefrom oxidation during deposition of the subsequent oxide layers whencarried out in an oxidizing atmosphere relative to the substrate andwill not provide a complete template for the epitaxial growth ofsubsequent layers. By heating a sol gel precursor film, and therebyallowing the precursor to flow into the substrate grain boundary areas,complete coverage can result. The heating can be relatively lowtemperature, for example, from about 80° C. to about 320° C., forexample, from about 100° C. to about 300° C., or from about 100° C. toabout 200° C. Such temperatures can be maintained from about 1 to about60 minutes, for example, from about 2 to about 45 minutes, or from about15 to about 45 minutes. The heating step can also be carried out usinghigher temperatures for a shorter time, for example, a film can beprocessed within two minutes at a temperature of 300° C.

[0112] This heating step can be carried out after, or concurrently with,the drying of excess solvent from the sol gel precursor film. It must becarried out prior to decomposition of the precursor film, however.

[0113] The carbon contamination accompanying conventional oxide filmpreparation in a reducing environment (e.g., 4%H₂—Ar) is believed to bethe result of an incomplete removal of the organic components of theprecursor film. The presence of carbon-containing contaminantsC_(x)H_(y) and C_(a)H_(b)O_(c) in or near the oxide layer can bedetrimental, since they can alter the epitaxial deposition of subsequentoxide layers. Additionally, it is likely that the trappedcarbon-containing contaminants buried in the film can be oxidized duringthe processing steps for subsequent oxide layers, which can utilizeoxidizing atmospheres. The oxidation of the carbon-containingcontaminants can result in CO₂ formation, and the subsequent blisteringof the film, and possible delamination of the film, or other defects inthe composite structure. Thus, it is undesirable to allowcarbon-containing contaminants arising from metal alkoxide decompositionto become oxidized only after the oxide layer is formed. Preferably, thecarbon-containing contaminants are oxidized (and hence removed from thefilm structure as CO₂) as the decomposition occurs. Also the presence ofcarbon-containing species on or near film surfaces can inhibit theepitaxial growth of subsequent oxide layers.

[0114] According to particular embodiments, after coating a metalsubstrate or buffer layer, the precursor solution can be air dried, andthen heated in an initial decomposition step. Alternatively, theprecursor solution can be directly heated in an initial decompositionstep, under an atmosphere that is reducing relative to the metalsubstrate. Once the oxide layer initially nucleates on the metalsubstrate in the desired epitaxial orientation, the oxygen level of theprocess gas is increased, for example, by adding water vapor or oxygen.The nucleation step requires from about 5 minutes to about 30 minutes totake place under typical conditions.

[0115] These methods are described in U.S. patent application Ser. No.09/617,520, filed on Jul. 14, 2000, and entitled “Enhanced Purity OxideLayer Formation,” which is hereby incorporated by reference.

[0116] In certain embodiments, an epitaxial buffer layer can be formedusing a low vacuum vapor deposition process (e.g., a process performedat a pressure of at least about 1×10⁻³ Torr),. The process can includeforming the epitaxial layer using a relatively high velocity and/orfocused gas beam of buffer layer material.

[0117] The buffer layer material in the gas beam can have a velocity ofgreater than about one meter per second (e.g., greater than about 10meters per second or greater than about 100 meters per second). At leastabout 50% of the buffer layer material in the beam can be incident onthe target surface (e.g., at least about 75% of the buffer layermaterial in the beam can be incident on the target surface, or at leastabout 90% of the buffer layer material in the beam can be incident onthe target surface).

[0118] The method can include placing a target surface (e.g., asubstrate surface or a buffer layer surface) in a low vacuumenvironment, and heating the target surface to a temperature which isgreater than the threshold temperature for forming an epitaxial layer ofthe desired material on the target surface in a high vacuum environment(e.g., less than about 1×10⁻³ Torr, such as less than about 1×10⁻⁴ Torr)under otherwise identical conditions. A gas beam containing the bufferlayer material and optionally an inert carrier gas is directed at thetarget surface at a velocity of at least about one meter per second. Aconditioning gas is provided in the low vacuum environment. Theconditioning gas can be contained in the gas beam, or the conditioninggas can be introduced into the low vacuum environment in a differentmanner (e.g., leaked into the environment). The conditioning gas canreact with species (e.g., contaminants) present at the target surface toremove the species, which can promote the nucleation of the epitaxialbuffer layer.

[0119] The epitaxial buffer layer can be grown on a target surface usinga low vacuum (e.g., at least about 1×10⁻³ Torr, at least about 0.1 Torr,or at least about 1 Torr) at a surface temperature below the temperatureused to grow the epitaxial layer using physical vapor deposition at ahigh vacuum (e.g., at most about 1×10⁻⁴ Torr). The temperature of thetarget surface can be, for example, from about 25° C. to about 800° C.(e.g., from about 500° C. to about 800° C., or from about 500° C. toabout 650° C.).

[0120] The epitaxial layer can be grown at a relatively fast rate, suchas, for example, at least about 50 Angstroms per second.

[0121] These methods are described in U.S. Pat. No. 6,027,564, issuedFeb. 22, 2000, and entitled “Low Vacuum Process for Producing EpitaxialLayers;” U.S. Pat. No. 6,022, 832, issued Feb. 8, 2000, and entitled“Low Vacuum Process for Producing Superconductor Articles with EpitaxialLayers;” and/or commonly owned U.S. patent application Ser. No.09/007,372, filed Jan. 15, 1998, and entitled “Low Vacuum Process forProducing Epitaxial Layers of Semiconductor Material,” all of which arehereby incorporated by reference.

[0122] In alternate embodiments, an epitaxial buffer layer can bedeposited by sputtering from a metal or metal oxide target at a highthroughput. Heating of the substrate can be accomplished by resistiveheating or bias and electric potential to obtain an epitaxialmorphology. A deposition dwell may be used to form an oxide epitaxialfilm from a metal or metal oxide target.

[0123] The oxide layer typically present on substrates can be removed byexposure of the substrate surface to energetic ions within a reducingenvironment, also known as Ion Beam etching. Ion Beam etching can beused to clean the substrate prior to film deposition, by removingresidual oxide or impurities from the substrate, and producing anessentially oxide-free preferably biaxially textured substrate surface.This improves the contact between the substrate and subsequentlydeposited material. Energetic ions can be produced by various ion guns,for example, which accelerate ions such as Ar⁺ toward a substratesurface. Preferably, gridded ion sources with beam voltages greater than150 ev are utilized. Alternatively, a plasma can be established in aregion near the substrate surface. Within this region, ions chemicallyinteract with a substrate surface to remove material from that surface,including metal oxides, to produce substantially oxide-free metalsurface.

[0124] Another method to remove oxide layers from a substrate is toelectrically bias the substrate. If the substrate tape or wire is madenegative with respect to the anode potential, it will be subjected to asteady bombardment by ions from the gas prior to the deposition (if thetarget is shuttered) or during the entire film deposition. This ionbombardment can clean the wire or tape surface of absorbed gases thatmight otherwise be incorporated in the film and also heat the substrateto elevated deposition temperatures. Such ion bombardment can be furtheradvantageous by improving the density or smoothness of the epitaxialfilm.

[0125] Upon formation of an appropriately textured, substantiallyoxide-free substrate surface, deposition of a buffer layer can begin.One or more buffer layers, each including a single metal or oxide layer,can be used. In some embodiments, the substrate is allowed to passthrough an apparatus adapted to carry out steps of the deposition methodof these embodiments. For example, if the substrate is in the form of awire or tape, the substrate can be passed linearly from a payout reel toa take-up reel, and steps can be performed on the substrate as it passesbetween the reels.

[0126] According to some embodiments, substrate materials are heated toelevated temperatures which are less than about 90% of the melting pointof the substrate material but greater than the threshold temperature forforming an epitaxial layer of the desired material on the substratematerial in a vacuum environment at the predetermined deposition rate.In order to form the appropriate buffer layer crystal structure andbuffer layer smoothness, high substrate temperatures are generallypreferred. Typical lower limit temperatures for the growth of oxidelayers on metal are approximately 200□ C. to 800□ C., preferably 500□ C.to 800□ C., and more preferably, 650□ C. to 800□ C. Various well-knownmethods such as radiative heating, convection heating, and conductionheating are suitable for short (2 cm to 10 cm) lengths of substrate, butfor longer (1 m to 100 m) lengths, these techniques may not be wellsuited. Also to obtain desired high throughput rates in a manufacturingprocess, the substrate wire or tape must be moving or transferringbetween deposition stations during the process. According to particularembodiments, the substrates are heated by resistive heating, that is, bypassing a current through the metal substrate, which is easily scaleableto long length manufacturing processes. This approach works well whileinstantaneously allowing for rapid travel between these zones.Temperature control can be accomplished by using optical pyrometers andclosed loop feedback systems to control the power supplied to thesubstrate being heated. Current can be supplied to the substrate byelectrodes which contact the substrate in at least two differentsegments of the substrate. For example, if the substrate, in the form ofa tape or wire, is passed between reels, the reels themselves could actas electrodes. Alternatively, if guides are employed to transfer thesubstrate between reels, the guides could act as electrodes. Theelectrodes could also be completely independent of any guides or reelsas well. In some embodiments, current is applied to the tape betweencurrent wheels.

[0127] In order that the deposition is carried out on tape that is atthe appropriate temperature, the metal or oxide material that isdeposited onto the tape is desirably deposited in a region between thecurrent wheels. Because the current wheels can be efficient heat sinksand can thus cool the tape in regions proximate to the wheels, materialis desirably not deposited in regions proximate to the wheels. In thecase of sputtering, the charged material deposited onto the tape isdesirably not influenced by other charged surfaces or materialsproximate to the sputter flux path. For this reason, the sputter chamberis preferably configured to place components and surfaces which couldinfluence or deflect the sputter flux, including chamber walls, andother deposition elements, in locations distant from the deposition zoneso that they do not alter the desired linear flux path and deposition ofmetal or metal oxide in regions of the tape at the proper depositiontemperature.

[0128] More details are provided in commonly owned U.S. patentapplication Ser. No. 09/500,701, filed on Feb. 9, 2000, and entitled“Oxide Layer Method,” and commonly owned U.S. patent application Ser.No. 09/615,669, filed on Jul. 14, 2000, and entitled “Oxide LayerMethod,” both of which are hereby incorporated by reference in theirentirety.

[0129] In certain embodiments, layer 16 can be conditioned (e.g.,thermally conditioned and/or chemically conditioned) so that layer 14 isformed on a conditioned surface. The conditioned surface of the layer 16can be biaxially textured (e.g., (113)[211]) or cube textured (e.g.,(100)[011] or (100)[011]), have peaks in an X-ray diffraction polefigure that have a full width at half maximum of less than about 20°(e.g., less than about 15°, less than about 10°, or from about 5° toabout 10°), be smoother than before conditioning as determined by highresolution scanning electron microscopy or atomic force microscopy, havea relatively high density, have a relatively low density of impurities,exhibit enhanced adhesion to other material layers (e.g., asuperconductor layer or a buffer layer) and/or exhibit a relativelysmall rocking curve width as measured by x-ray diffraction.

[0130] “Chemical conditioning” as used herein refers to a process whichuses one or more chemical species (e.g., gas phase chemical speciesand/or solution phase chemical species) to affect changes in the surfaceof a material layer, such as a buffer layer or a superconductor materiallayer, so that the resulting surface exhibits one or more of the abovenoted properties.

[0131] “Thermal conditioning” as used herein refers to a process whichuses elevated temperature, with or without chemical conditioning, toaffect changes in the surface of a material layer, such as a bufferlayer or a superconductor material layer, so that the resulting surfaceexhibits one or more of the above noted properties. Thermal conditioningcan be performed with or without the use of chemical conditioning.Preferably, thermal conditioning occurs in a controlled environment(e.g., controlled gas pressure, controlled gas environment and/orcontrolled temperature).

[0132] Thermal conditioning can include heating the surface of the layer16 to a temperature at least about 5° C. above the depositiontemperature or the crystallization temperature of the underlying layer(e.g., from about 15° C. to about 500° C. above the depositiontemperature or the crystallization temperature of the underlying layer,from about 75° C. to about 300° C. above the deposition temperature orthe crystallization temperature of the underlying layer, or from about150° C. to about 300° C. above the deposition temperature or thecrystallization temperature of the underlying layer). Examples of suchtemperatures are from about 500° C. to about 1200° C. (e.g., from about800° C. to about 1050° C.). Thermal conditioning can be performed undera variety of pressure conditions, such as above atmospheric pressure,below atmospheric pressure, or at atmospheric pressure. Thermalconditioning can also be performed using a variety of gas environments,such as a chemical conditioning environment (e.g., an oxidizing gasenvironment, a reducing gas environment) or an inert gas environment.

[0133] “Deposition temperature” as used herein refers to the temperatureat which the layer being conditioned was deposited.

[0134] “Crystallization temperature” as used herein refers to thetemperature at which a layer of material (e.g., the underlying layer)takes on a crystalline form.

[0135] Chemical conditioning can include vacuum techniques (e.g.,reactive ion etching, plasma etching and/or etching with fluorinecompounds, such as BF₃ and/or CF₄). Chemical conditioning techniques aredisclosed, for example, in Silicon Processing for the VLSI Era, Vol. 1,eds. S. Wolf and R. N. Tanber, pp. 539-574, Lattice Press, Sunset Park,Calif., 1986.

[0136] Alternatively or additionally, chemical conditioning can involvesolution phase techniques, such as disclosed in Metallurgy andMetallurgical Engineering Series, 3d ed., George L. Kehl, McGraw-Hill,1949. Such techniques can include contacting the surface of theunderlying layer with a relatively mild acid solution (e.g., an acidsolution containing less about 10 percent acid, less than about twopercent acid, or less than about one percent acid). Examples of mildacid solutions include perchloric acid, nitric acid, hydrofluoric acid,hydrochloric acid, acetic acid and buffered acid solutions. In oneembodiment, the mild acid solution is about one percent aqueous nitricacid. In certain embodiments, bromide-containing and/orbromine-containing compositions (e.g., a liquid bromine solution) can beused to condition the surface of a buffer layer or a superconductorlayer.

[0137] These methods are described in commonly owned U.S. ProvisionalPatent Application No. 60/166,140, filed Nov. 18, 1999, and entitled“Multi-Layer Articles and Methods of Making Same,” and commonly ownedU.S. patent application Ser. No. 09/615,999, filed on Jul. 14, 2000, andentitled “Multi-layer Articles and Methods of Making Same,” both ofwhich are hereby incorporated by reference.

[0138] Alternatively, layer 16 can be formed of a superconductormaterial, which can be prepared as described above. In embodiments inwhich layer 16 is formed of a superconductor material, the relativethickness of layers 16 and 14 can vary depending upon the method used toprepare article 20 and/or the intended use of article 20. For example,layer 14 can be thicker than layer 16, or layer 16 can be thicker thanlayer 14. For example, in some embodiments, layer 16 can have athickness of less than about one micrometer (e.g., less than about 0.5micrometer, such as from about 0.05 micrometer to about 0.2 micrometer),and layer 14 can have a thickness of greater than about one micrometer(e.g., greater than about two micrometers, greater than about threemicrometers, greater than about four micrometers, greater than aboutfive micrometers).

[0139] In embodiments in which layer 16 is formed of a superconductormaterial, the combined thickness of layers 14 and 16 can vary dependingupon the methods used to prepare article 20 and/or the intended use ofarticle 20. For example, the combined thickness of layers 14 and 16 canbe less than two micrometers or greater than two micrometers.Preferably, the combined thickness of layers 14 and 16 is greater thanabout one micrometer (e.g., greater than about two micrometers, greaterthan about three micrometers, greater than about four micrometers,greater than about five micrometers, greater than about six micrometers,greater than about seven micrometers, greater than about eightmicrometers, greater than about nine micrometers, greater than about 10micrometers).

[0140] In embodiments in which layer 16 is formed of a superconductormaterial, the surface of layer 16 can be chemically and/or thermallyconditioned as described above.

[0141] In certain embodiments, where layer 16 is formed of asuperconductor material, layer 14 can be from solid-state, or semi solidstate, precursor materials deposited in the form of a dispersion. Theseprecursor solutions allow for example the substantial elimination ofBaCO₃ formation in final YBCO superconducting layers, while alsoallowing control of film nucleation and growth.

[0142] Two general approaches are presented for the formulation ofprecursor solutions. In one approach, the cationic constituents of theprecursor solution are provided in components taking on a solid form,either as elements, or preferably, compounded with other elements. Theprecursor solution is provided in the form of ultrafine particles whichare dispersed so that they can be coated onto and adhere onto thesurface of a suitable substrate, intermediate-coated substrate, orbuffer-coated substrate. These ultrafine particles can be created byaerosol spray, by evaporation or by similar techniques which can becontrolled to provide the chemical compositions and sizes desired. Theultrafine particles are less than about 500 nm, preferably less thanabout 250 nm, more preferably less than about 100 nm and even morepreferably less than about 50 nm. In general, the particles are lessthan about 50% the thickness of the desired final film thickness,preferably less than about 30% most preferably less than about 10% ofthe thickness of the desired final film thickness. For example, theprecursor solution can comprise ultrafine particles of one or more ofthe constituents of the superconducting layer in a substantiallystoichiometric mixture, present in a carrier. This carrier comprises asolvent, a plasticizer, a binder, a dispersant, or a similar systemknown in the art, to form a dispersion of such particles. Each ultrafineparticle can contain a substantially compositionally uniform,homogeneous mixture of such constituents. For example, each particle cancontain BaF₂, and rare-earth oxide, and copper oxide or rareearth/barium/copper oxyhalide in a substantially stoichiometric mixture.Analysis of such particles would desirably reveal arare-earth:barium:copper ratio as substantially 1:2:3 in stoichiometry,with a fluorine:barium ratio of substantially 2:1 in stoichiometry.These particles can be either crystalline, or amorphous in form.

[0143] In a second approach, the precursor components can be preparedfrom elemental sources, or from a substantially stoichiometric compoundcomprising the desired constituents. For example, evaporation of a solidcomprising a substantially stoichiometric compound of desired REBCOconstituents (for example, YBa₂Cu₃O_(7−x)) or a number of solids, eachcontaining a particular constituent of the desired final superconductinglayer (for example, Y₂O₃, BaF₂, CuO) could be used to produce theultrafine particles for production of the precursor solutions.Alternatively, spray drying or aerosolization of a metalorganic solutioncomprising a substantially stoichiometric mixture of desired REBCOconstituents could be used to produce the ultrafine particles used inthe precursor solutions. Alternatively, one or more of the cationicconstituents can be provided in the precursor solution as a metalorganicsalt or metalorganic compound, and can be present in solution. Themetalorganic solution can act as a solvent, or carrier, for the othersolid-state elements or compounds. According to this embodiment,dispersants and/or binders can be substantially eliminated from theprecursor solution. For example, the precursor solution can compriseultrafine particles of rare-earth oxide and copper oxide insubstantially a 1:3 stoichiometric ratio, along with a solublizedbarium-containing salt, for example, barium-trifluoroacetate dissolvedin an organic solvent, such as methanol.

[0144] The precursor solutions can be applied to substrate orbuffer-treated substrates by a number of methods, which are designed toproduce coatings of substantially homogeneous thickness. For example,the precursor solutions can be applied using spin coating, slot coating,gravure coating, dip coating, tape casting, or spraying. The substrateis desirably uniformly coated to yield a superconducting film of fromabout one to 10 micrometers (e.g., at least about one micrometer, atleast about two micrometers, at least about three micrometers, at leastabout four micrometers, at least about five micrometers).

[0145] More details are provided in commonly owned U.S. patentapplication Ser. No. 09/500,717, filed on Feb. 9, 2000, and entitled“Coated Conductor Thick Film Precursor,” which is hereby incorporated byreference in its entirety.

[0146] In embodiments in which layer 16 is formed of a superconductormaterial, the critical current density of the combined layers 14 and 16in article 20 can be relatively high. Preferably, the critical currentdensity of the combined layers 14 and 16 in article 20 is at least about5×10⁵ Amperes per square centimeter, more preferably at least about1×10⁶ Amperes per square centimeter, such as at least about 2×10⁶Amperes per square centimeter as determined by transport measurement at77K in self field using a 1 micro Volt per centimeter criterion.

[0147] While the foregoing discussion has described multi-layer articleshaving two layers of material (i.e., no intermediate layer) and threelayers of material (i.e., one intermediate layer), the invention is notlimited in this sense. Instead, multiple intermediate layers can beused. Each of the intermediate layers can be formed of a buffer layermaterial or a superconductor material. For example, FIG. 3 shows amulti-layer superconductor 30 according to yet another embodiment of theinvention. Article 30 includes layers 12, 14 and 16. Article 30 furtherincludes an additional intermediate layer(s) 18 and 22 having surfaces19 and 23, respectively. Layers 18 and 22 are disposed between layers 16and 14. Each of layers 16, 18 and 22 can be formed of a buffer layermaterial or a superconductor material. Moreover, surfaces 19 and 23 canbe prepared using the methods discussed herein.

[0148] In some embodiments, a superconductor article includes threebuffer layers between the substrate and superconductor material. A layerof Y₂O₃ or CeO₂ (e.g., from about 20 nanometers to about 50 nanometersthick) is deposited (e.g., using electron beam evaporation) onto thesubstrate surface, or a layer of Gd₂O₃ is deposited from solution. Alayer of YSZ (e.g., from about 0.2 micrometer to about 1 micrometerthick, such as about 0.5 micrometer thick) is deposited onto the surfaceof the Y₂O₃, CeO₂ or Gd₂O₃ layer using sputtering (e.g, using magnetronsputtering). A CeO₂ layer (e.g., about 20 nanometers thick) is deposited(e.g, using magnetron sputttering) onto the YSZ surface, or a layer ofGd₂O₃ is deposited from solution onto the YSZ surface. One or more ofthe buffer layers can be chemically and/or thermally conditioned asdescribed herein.

[0149] Superconductor articles according to the invention can alsoinclude a layer of a cap material which can be formed of a metal oralloy whose reaction products with the superconductor material (e.g.,YBa₂Cu₃O_(7−x)) are thermodynamically unstable under the reactionconditions used to form the layer of cap material. Exemplary capmaterials include silver, gold, palladium and platinum.

[0150] In addition, while the foregoing discussion has describedmulti-layer articles having certain structures, the invention is notlimited in this sense. For example, in some embodiments, multi-layerhigh temperature superconductors are provided, including first andsecond high temperature superconductor coated elements. Each elementincludes a substrate, at least one buffer layer deposited on thesubstrate, a high temperature superconductor layer, and optionally a caplayer. The first and second high temperature superconductor coatedelements can be joined at the first and second cap layers, or can bejoined with an intervening, preferably metallic, layer. Exemplaryjoining techniques include soldering and diffusion bonding.

[0151] Such a multi-layer architecture can provide improved currentsharing, lower hysteretic losses under alternating current conditions,enhanced electrical and thermal stability, and improved mechanicalproperties. Useful conductors can be made having multiple tapes stackedrelative to one another and/or laminated to provide sufficient ampacity,dimensional stability, and mechanical strength. Such embodiments alsoprovide a means for splicing coated tape segments and for termination ofcoated tape stackups or conductor elements.

[0152] Moreover, it is expected that this architecture can providesignificant benefits for alternating current applications. AC losses areshown to be inversely proportional to the effective critical currentdensity within the conductor, more specifically, the cross-sectionalarea within which the current is carried. For a multifilimentaryconductor, this would be the area of the “bundle” of superconductingfilaments, excluding any sheath material around that bundle. For a“face-to-face” architecture, the “bundle” critical current density wouldencompass only the high temperature superconductor films and thethickness of the cap layer structure. The cap layer can be formed of oneor more layers, and preferably includes at least one noble metal layer.“Noble metal,” as used herein, is a metal, the reaction products ofwhich are thermodynamically unstable under the reaction conditionsemployed to prepare the HTS tape. Exemplary noble metals include, forexample, silver, gold, palladium, and platinum. Noble metals provide alow interfacial resistance between the HTS layer and the cap layer. Inaddition, the cap layer can include a second layer of normal metal (forexample, copper or aluminum or alloys of normal metals). In directcurrent applications, additional face-to-face wires would be bundled orstacked to provide for the required ampacity and geometry for a givenapplication.

[0153] Additionally, the high temperature superconductor film on thesurface of the tapes could be treated to produce local breaks, that is,non-superconducting regions or stripes in the film only along the lengthof the tape (in the current flow direction). The cap layer deposited onthe high temperature superconductor film would then serve to bridge thenonsuperconducting zones with a ductile normal metal region. An offsetin the edge justification of the narrow strips or filaments, similar toa running bond brick pattern, would allow current to transfer to severalnarrow superconducting filaments both across the cap layers and toadjacent filaments, further increasing the redundancy and improvingstability.

[0154] In all embodiments, a normal metal layer could be included alongthe edge of the conductor to hermetically seal the high temperaturesuperconductor films and to provide for current transfer into the film,and if necessary, from the film into the substrate.

[0155] More details are provided in commonly owned U.S. ProvisionalPatent Application Ser. No. 60/145,468, filed on Jul. 23, 1999, andentitled “Enhanced High Temperature Coated Superconductors,” andcommonly owned U.S. patent application Ser. No. 09/617,518, filed onJul. 14, 2000, and entitled “Enhanced High Temperature CoatedSuperconductors,” both of which are hereby incorporated by reference inits entirety.

[0156] In some embodiments, coated conductors can be fabricated in a waythat minimizes losses incurred in alternating current applications. Theconductors are fabricated with multiple conducting paths, each of whichcomprises path segments which extend across at least two conductinglayers, and further extend between these layers.

[0157] Each superconducting layer has a plurality of conductive pathsegments extending across the width of the layer, from one edge toanother, and the path segments also have a component of direction alongthe length of the superconducting layer. The path segments in thesuperconducting layer surface are in electrically conductivecommunication with interlayer connections, which serve to allow currentto flow from one superconducting layer to another. Paths, which are madeup of path segments, are periodically designed, so that current flowgenerally alternates between two superconducting layers in bilayeredembodiments, and traverses the layers through interlayer connections.

[0158] Superconducting layers can be constructed to contain a pluralityof path segments which extend both across their widths and along theirlengths. For example, superconducting layers can be patterned so as toachieve a high resistivity or a fully insulating barrier between each ofthe plurality of path segments. For example, a regular periodic array ofdiagonal path segments can be imposed on the layer along the full lengthof the tape. Patterning of superconducting layers to give such arrayscan be accomplished by a variety of means known to those skilled in theart, including for example, laser scribing, mechanical cutting,implantation, localized chemical treatment through a mask, and otherknown methods. Further, the superconducting layers are adapted to allowthe conductive path segments in their surfaces to electricallycommunicate with conducting interlayer connections passing between thelayers, at or near their edges. The interlayer connections willtypically be normally conducting (not superconducting) but in specialconfigurations could also be superconducting. Interlayer connectionsprovide electrical communication between superconducting layers whichare separated by non-conducting or highly resistive material which ispositioned between the superconducting layers. Such non-conducting orhighly resistive material can be deposited on one superconducting layer.Passages can be fabricated at the edges of the insulating material toallow the introduction of interlayer connections, followed by depositionof a further superconducting layer. One can achieve a transposedconfiguration with coated conductors by patterning a superconductinglayer into filaments parallel to the axis of the tape and winding thetape in a helical fashion around a cylindrical form.

[0159] More details are provided in commonly owned U.S. patentapplication Ser. No. 09/500,718, filed on Feb. 9, 2000, and entitled“Coated Conductors with Reduced AC Loss,” which is hereby incorporatedby reference in its entirety.

[0160] The following examples are illustrative only.

EXAMPLE I

[0161] A precursor solution was prepared as follows. About 1.36 grams ofY(CF₃CO₂)₃ 4H₂O, about 2.46 grams of Ba(CF₃CO₂)₂ and about 2.51 grams ofCu(CF₃CO₂)₂2H₂O were dissolved in about 5 milliliters of CH₃OH. About0.86 milliliters of water was then added and the total volume of thesolution was adjusted to about 10 milliliters with methanol.

[0162] The precursor solution was spin coated onto the (100) surface ofa single crystal SrTiO₃ substrate as follows. The substrate was rampedfrom about zero revolutions per minute (RPM) to about 2000 RPM in about0.5 seconds. The spin speed was held at about 2000 RPM for about fiveseconds, and then ramped to about 4000 RPM in about 0.5 seconds. Thespin speed was held at about 4000 RPM for about 60 seconds, then reducedto about zero RPM.

[0163] The coated sample was decomposed as follows. The sample washeated from room temperature to about 210° C. at a rate of about 10° C.per minute in a nominal gas environment having a total gas pressure ofabout 760 Torr (water vapor pressure of about 24 Torr and balanceoxygen). Heating was conducted in an about 2.25″ diameter furnace usinga gas flow rate of about 4.5 standard cubic feet per hour. While keepingsubstantially the same nominal gas environment, the temperature wasincreased to about 220° C. at a rate of about 0.5° C. per minute,followed by heating to about 400° C. at a rate of about 5° C. per minuteto form an intermediate thin film.

[0164] After decomposition, the intermediate film was heated to about725° C. at a rate of about 10° C. per minute and held for about threehours in an environment having a nominal total gas pressure of about 760Torr (water vapor pressure of about 17 Torr, oxygen gas pressure ofabout 76 millitorr and balance oxygen) followed by holding thetemperature at about 725° C. for about 10 minutes in an environmenthaving a nominal total gas pressure of about 760 Torr (oxygen gaspressure of about 76 millitorr and balance nitrogen). The film wascooled to about 450° C. in the same nominal gas environment and was heldat this temperature for about an hour in a gas environment having anominal total gas pressure of about 760 Torr (about 760 Torr oxygen) andsubsequently cooled to room temperature.

[0165] The resulting layer was (001) textured YBa₂Cu₃O_(7−x) and about0.4 micrometers thick.

EXAMPLE II

[0166] A precursor solution was prepared as follows. About 1.41 grams ofY(CF₃CO₂)₃, about 2.39 grams of Ba(CF₃CO₂)₂ and about 1.97 grams ofCu(CH₃CO₂)₂2H₂O were dissolved in about 20 milliliters of CH₃OH, about10 milliliters of water and about 0.5 milliliters of NH₄OH. Thissolution was then concentrated to about 20 milliliters by removal ofsolvent under vacuum.

[0167] The concentrated precursor solution was spin coated onto the(100) surface of a single crystal SrTiO₃ substrate and decomposed asdescribed in Example I to form a film of an intermediate.

[0168] The thickness of the film of the intermediate was about 0.95micrometers. FIG. 4 is an optical micrograph of the film(750×magnification), showing that the film had no visible cracks orblisters.

[0169] The decomposed film was then reacted as in Example I to form aYBa₂Cu₃O_(7−x) film.

EXAMPLE III

[0170] Example II was repeated, except that spin rates of 500 RPM ratherthan 2000 RPM, and 1000 RPM rather than 4000 RPM were used. Afterdecomposition of the precursor film, the intermediate film was about 1.4micrometers thick. The film was further reacted as in Example I to forma YBa₂Cu₃O_(7−x) film. FIG. 5 is a θ-2θ X-ray diffraction scan of theYBa₂Cu₃O_(7−x) film, showing substantial formation of texturedYBa₂Cu₃O_(7−x) along with minor unidentified impurity phases.

EXAMPLE IV

[0171] A precursor solution was prepared as follows. About 1.98 grams ofCu(CCl₃CO₂)₂ xH₂O was dissolved in about 10 milliliters of methanol.About 2.46 grams of Y(CF₃CO₂)₃ and about 1.20 grams of Ba(CF₃CO₂)₂ wereadded while stirring. The solution was concentrated to about fivemilliliters by evaporation of solvent under vacuum. The concentratedsolution was viscous and deep blue colored.

[0172] The concentrated precursor solution was spin coated onto the(100) surface of a single crystal SrTiO₃ substrate as described inExample III, except that the spin rates were 1000 RPM rather than 500RPM, and 2000 RPM rather than 1000 RPM. The precursor film was thendecomposed as described in Example I.

[0173] After decomposition of the precursor film, the intermediate filmwas about three to about four micrometers thick and had no visibledefects. The intermediate film was further reacted as in Example I toform a YBa₂Cu₃O_(7−x) film. FIG. 6 is a θ-2θ X-ray diffraction scan ofthe YBa₂Cu₃O_(7−x) film, showing substantial formation of texturedYBa₂Cu₃O_(7−x) along with minor unidentified impurity phases.

EXAMPLE V

[0174] Example IV was repeated, except that spin rates of 500 RPM ratherthan 1000 RPM, and 1000 RPM rather than 2000 RPM were used. Afterdecomposition of the precursor film, the intermediate film was greaterthan about four micrometers thick. The intermediate film was Furtherreacted as in Example I to form a YBa₂Cu₃O_(7−x) film.

EXAMPLE VI

[0175] A precursor solution prepared as in Example I was spin coatedonto a CeO₂ capped YSZ single crystal substrate as described in ExampleI, but using spin rates of 1000 RPM rather than 2000 RPM, and 2000 RPMrather than 4000 RPM. The precursor film was decomposed by introducingthe precursor to the furnace at 100° C. under a gas environment having atotal pressure of about 760 Torr (about 29 Torr H₂O and the balance O₂).The furnace was heated to about 400° C. at about 5° C. per minute, andheld at 400° C. for about 30 minutes, then cooled to room temperature,forming a film of an intermediate material. FIG. 7 is an opticalmicrograph of the film of the intermediate material (750×magnification),showing that film contained many visible defects.

EXAMPLE VII

[0176] A precursor solution prepared as in Example IV was spin coatedonto a CeO₂ capped YSZ single crystal substrate as described in ExampleIV. The precursor film was decomposed by introducing the precursor tothe furnace at 300° C. under a gas environment having a total pressureof about 760 Torr (about 29 Torr H₂O and the balance O₂). The furnacewas heated to about 400° C. at about 5° C. per minute, and held at 400°C. for about 30 minutes, then cooled to room temperature, forming a filmof an intermediate material. FIG. 8 is an optical micrograph of the filmof the intermediate material (750×magnification), showing that the filmcontained no visible defects.

EXAMPLE VIII

[0177] A precursor solution prepared as in Example IV was spin coatedonto a CeO₂ capped YSZ single crystal substrate as described in ExampleIV. The precursor film was decomposed by introducing the precursor tothe furnace at 400° C. under the gas environment described in ExampleVI. The furnace was held at about 400° C. for about 30 minutes, thencooled to room temperature, forming a film of an intermediate material.FIG. 9 is an optical micrograph of the film of the intermediatematerial, showing that the film contained no visible defects.

EXAMPLE IX

[0178] A precursor solution was prepared as follows. About five grams oftrichloroacetic acid (CCl₃CO₂)H was dissolved in about five millilitersof methanol. About 1.974 grams of Cu(O₂C—CH₃)₂ 2H₂O, about 1.022 gramsof Ba(0 ₂C—CH₃)₂ and about 0.6762 grams of Y(O₂C—CH₃)₃4H₂O were addedsequentially to the trichloroacetate/methanol mixture. This mixture wasthen dried under vacuum, and three grams of the dried solid weredissolved in about five milliliters of methanol to form the precursorsolution.

[0179] The precursor solution was spin coated onto a CeO₂ capped YSZsingle crystal substrate as described in Example IV. The precursor filmwas then decomposed as described in Example I to form a film of anintermediate material. FIG. 10 is an optical micrograph of the film ofthe intermediate material (37×magnification), showing that the filmcontained no visible defects.

EXAMPLE X

[0180] A precursor solution was prepared as follows.

[0181] About 8.55 grams of Y(CF₃CO₂)₃ and about 14.5321 grams ofBa(CF₃CO₂)₂ were dissolved in about 50 milliliters of methanol to formone solution.

[0182] Another solution was formed as follows. About 11.98 grams ofCu(CH₃CO₂)₂ H₂O was dispersed in about 10 milliliters of methanol andheated under reflux for about 10 minutes. About 20 milliliters ofC₂H₅COOH was then added drop wise and boiled under reflux for about 30minutes, followed by cooling to about room temperature.

[0183] The above two solutions were mixed together under stirring forabout 10 minutes and then concentrated to about 50 milliliters byremoval of solvent under vacuum.

[0184] The resulting, concentrated solution was spin coated onto a CeO₂capped YSZ single crystal substrate using the spin coating parametersdescribed in Example I.

[0185] The coated sample was decomposed as follows. The sample wasintroduced into the furnace by introducing to the furnace described inExample I at about 200° C. under in a nominal gas environment having atotal pressure of about 760 torr (about 17 torr H₂O and balance O₂). Thefurnace was then heated to about 250° C. at rate of about 1° C. perminute. The sample was further heated to about 400° C. at a rate ofabout 10° C. per minute (in the same nominal gas environment), and thencooled to room temperature (in the same nominal gas environment) to forma film of an intermediate material.

[0186] After decomposition, the intermediate film was further reacted asdescribed in Example I to form a YBa₂Cu₃O_(7−x) layer. FIG. 11 is theθ-2θ X-ray diffraction scan of the YBa₂Cu₃O_(7−x) layer, showingformation of high quality (001) textured YBa₂Cu₃O_(7−x) layer which isabout 0.41 micrometer thick. The YBa₂Cu₃O_(7−x) layer had a criticalcurrent density of about 4.2×10⁶ Amperes per square centimeter at 77K(self field).

EXAMPLE XI

[0187] A concentrated precursor solution was prepared as described inExample X. The concentrated precursor solution was spin coated onto aCeO₂ capped YSZ single crystal substrate using the spin coatingparameters described in Example I except that the spin rates were 1500RPM rather than 2000 RPM, and 3000 RPM rather than 4000 RPM. The spincoated film was decomposed as described in Example X, and theintermediate film was further reacted as described in Example 1. Theresulting layer was (001) textured YBa₂Cu₃O_(7−x) and about 0.5micrometer thick. The YBa₂Cu₃O_(7−x) layer had a critical currentdensity of about 3.2×10⁶ Amperes per square centimeter 77K (self field).

EXAMPLE XII

[0188] A precursor solution was prepared as follows.

[0189] A first solution was formed by dispersing about 1.35 grams ofY(CH₃CO₂)₃4H₂O in about 10 milliliters of methanol. About fivemilliliters of C₂H₅COOH and about three milliliters of NH₄OH were addedunder stirring until the solution became clear.

[0190] A second solution was formed by dissolving about 2.9 grams ofBa(CF₃CO₂)₂ in about 10 milliliters of CH₃ 0H.

[0191] A third solution was formed by dispersing about 2.4 grams ofCu(CH₃CO₂)₂.H₂O in about 10 ml of methanol. About five milliliters ofC₂H₅COOH and about three milliliters of NH4OH were added drop wise untilthe solution became clear.

[0192] The above three solutions of were mixed together under stirringfor about 10 minutes and then concentrated to about 10 milliliters byremoval of solvent under vacuum.

[0193] The resulting concentrated solution was spin coated onto a CeO₂capped YSZ single crystal substrate using the spin coating parametersdescribed in Example I. The coated film was decomposed as described inExample X. After decomposition, the intermediate film was furtherreacted as described in Example I to form a YBa₂Cu₃O_(7−x) layer. FIG.12 is the θ-2θ X-ray diffraction scan of the YBa₂Cu₃O_(7−x) layer. TheYBa₂Cu₃O_(7−x) layer had a high quality (001) texture and was about 0.3micrometer thick. The YBa₂Cu₃O_(7−x) layer had a critical currentdensity of about 4.8×10⁶ Amperes per square centimeter at 77K (selffield).

Example XIII

[0194] A precursor solution was prepared as follows. About 8.55 grams ofY(CF₃CO₂)₃, about 14.53 grams of Ba(CF₃CO₂)₂ and about 12.87 grams ofCu(C₂H₅CO₂)₂ were dissolved in about 60 milliliters of methanol. Thesolution was then concentrated to about 50 milliliters by removal ofsolvent under vacuum.

[0195] The concentrated precursor solution was spin coated onto a CeO₂capped YSZ single crystal substrate using the spin coating parametersdescribed in Example I. The coated film was decomposed as described inExample X. After decomposition, the intermediate film was furtherreacted as described in Example I to form a YBa₂Cu₃O_(7−x) layer. FIG.13 is the θ-2θ X-ray diffraction scan of the YBa₂Cu₃O_(7−x) layer. TheYBa₂Cu₃O_(7−x) layer had a high quality (001) texture and was about 0.8micrometer thick. The YBa₂Cu₃O_(7−x) layer had a critical currentdensity of about 3.8×10⁶ Amperes per square centimeter at 77K (selffield) and a critical current of about 300 Amperes per centimeter width.

EXAMPLE XIV

[0196] A precursor solution was prepared as described in Example XIII.The precursor solution was deposited onto a continuous length of a metaltape substrate using a slot die coater.

[0197] The metal tape substrate was formed of four layers. The firstlayer was deformation textured nickel having a thickness of about 50micrometers and a thickness of about 10 millimeters. An about 50nanometer thick epitaxial layer of Gd₂O₃ was disposed on the texturedsurface of the nickel. An about 250 nanometer thick epitaxial layer ofYSZ was disposed on the Gd₂O₃ layer. An about 24 nanometer thickepitaxial layer of CeO₂ layer was disposed on the YSZ layer.

[0198] The precursor film was deposited in an atmosphere containingabout 11 torr H₂O and the balance nitrogen (total pressure of about 760torr).

[0199] The precursor coated film was decomposed by transporting thecoated tape through a tube furnace having a diameter of about 2.5inches. The tube furnace had temperature and gas environment gradients.The sample was passed through the tube furnace at a transport rate sothat the processing of the sample (i.e., temperatures and gasenvironments to which the sample was exposed during processing) wassubstantially the same as described in Example X.

[0200] The resulting YBa₂Cu₃O_(7−x) film was about 0.8 micrometers thickand had no visible defects.

[0201] While certain embodiments have been described herein, theinvention is not limited to these embodiments. Other embodiments are inthe claims.

What is claimed is:
 1. A method, comprising: disposing a precursorsolution onto a surface of a layer to form a precursor film, theprecursor film including a salt of a rare earth metal, a salt of analkaline earth metal and a carboxylate salt of a transition metal, withthe proviso that the carboxylate salt of the transition metal salt isnot a trifluoroacetate salt of the transition metal; and treating theprecursor film to form an intermediate of a rare earth metal-alkalineearth metal-transition metal oxide.
 2. The method of claim 1, whereinthe precursor film is treated for less than about five hours.
 3. Themethod of claim 1, the precursor solution further comprises a Lewisbase.
 4. The method of claim 3, wherein the Lewis base comprises anitrogen-containing compound.
 5. The method of claim 4, wherein thenitrogen-containing compound is selected from the group consisting ofammonia and amines.
 6. The method of claim 1, wherein the layer of theintermediate has a thickness of at least about one micrometer.
 7. Themethod of claim 1, further comprising treating the layer of theintermediate to form a layer of a rare earth metal-alkaline earthmetal-transition metal oxide having a critical current density of atleast about 0.5×10⁶ Amperes per square centimeter.
 8. The method ofclaim 1, wherein defects contained within the layer of the intermediatecomprise less than about 20 percent of any volume element of theintermediate defined by a projection of one square centimeter of asurface of the intermediate.
 9. The method of claim 1, wherein thecarboxylate salt of the transition metal comprises Cu(O₂CC₂H₅)₂.
 10. Themethod of claim 9, wherein the alkaline earth metal salt comprisesbarium trifluoroacetate.
 11. The method of claim 10, wherein the rareearth metal salt comprises a salt selected from the group consisting ofhalogenated yttrium carboxylates and nonhalogenated yttriumcarboxylates.
 12. The method of claim 1, wherein the carboxylate salt ofthe transition metal comprises a nonhalogenated carboxylate salt. 13.The method of claim 12, wherein the alkaline earth metal salt comprisesbarium trifluoroacetate.
 14. The method of claim 13, wherein the rareearth metal salt comprises a salt selected from the group consisting ofhalogenated yttrium acetates and nonhalogenated yttrium acetates.
 15. Amethod, comprising: disposing a precursor solution onto a surface of alayer to form a precursor film, the precursor film including a salt of arare earth metal, a salt of an alkaline earth metal and a carboxylatesalt of copper; and treating the precursor film to form an intermediateof a rare earth metal-alkaline earth metal-transition metal oxide. 16.The method of claim 15, wherein the precursor film is treated for lessthan about five hours.
 17. The method of claim 15, wherein the precursorsolution further comprises a Lewis base.
 18. The method of claim 17,wherein the Lewis base comprises a nitrogen-containing compound.
 19. Themethod of claim 18, wherein the nitrogen-containing compound is selectedfrom the group consisting of ammonia and amines.
 20. The method of claim15, wherein the layer of the intermediate has a thickness of at leastabout two micrometers.
 21. The method of claim 15, wherein the layer ofthe intermediate has a thickness of at least about three micrometers.22. The method of claim 15, wherein the layer of the intermediate has athickness of at least about four micrometers.
 23. The method of claim15, wherein the layer of the intermediate has a thickness of at leastabout five micrometers.
 24. The method of claim 15, further comprisingtreating the layer of the intermediate to form a layer of a rare earthmetal-alkaline earth metal-transition metal oxide material having acritical current density of at least about 0.5×10⁶ Amperes per squarecentimeter.
 25. The method of claim 15, wherein defects contained withinthe layer of the intermediate comprise less than about 20 percent of anyvolume element of the intermediate defined by a projection of one squarecentimeter of a surface of the intermediate.
 26. The method of claim 15,wherein the carboxylate salt of copper comprises Cu(O₂CC₂H₅)₂.
 27. Themethod of claim 26, wherein the alkaline earth metal salt comprisesbarium trifluoroacetate.
 28. The method of claim 27, wherein the rareearth metal salt comprises a salt selected from the group consisting ofhalogenated yttrium acetates and nonhalogenated yttrium acetates. 29.The method of claim 15, wherein the carboxylate salt of copper comprisesa nonhalogenated carboxylate salt of copper.
 30. The method of claim 29,wherein the alkaline earth metal salt comprises barium trifluoroacetate.31. The method of claim 30, wherein the rare earth metal salt comprisesa salt selected from the group consisting of halogenated yttriumacetates and nonhalogenated yttrium acetates.
 32. A method, comprising:disposing a precursor solution onto a surface of a layer to form aprecursor film, the precursor film including a salt of a rare earthmetal, a salt of an alkaline earth metal and a carboxylate salt of atransition metal; and treating the precursor film to form a rare earthmetal-alkaline earth metal-transition metal oxide intermediate.
 33. Themethod of claim 32, wherein the precursor film is treated for less thanabout five hours.
 34. The method of claim 32, wherein the precursorsolution further comprises a Lewis base.
 35. The method of claim 32,wherein the Lewis base comprises a nitrogen-containing compound.
 36. Themethod of claim 32, wherein the nitrogen-containing compound is selectedfrom the group consisting of ammonia and amines.
 37. The method of claim32, wherein the superconductor material has a critical current densityof at least about 1×10⁶ Amperes per square centimeter.
 38. The method ofclaim 32, wherein the intermediate is at least about one micrometerthick.
 39. The method of claim 32, wherein the carboxylate salt of thetransition metal comprises Cu(O₂CC₂H₅)₂.
 40. The method of claim 39,wherein the alkaline earth metal salt comprises barium trifluoroacetate.41. The method of claim 40, wherein the rare earth metal salt comprisesa salt selected from the group consisting of halogenated yttriumacetates and nonhalogenated yttrium acetates.
 42. The method of claim32, wherein the carboxylate salt of the transition metal comprises anonhalogenated carboxylate salt.
 43. The method of claim 42, wherein thealkaline earth metal salt comprises barium trifluoroacetate.
 44. Themethod of claim 43, wherein the rare earth metal salt comprises a saltselected from the group consisting of halogenated yttrium acetates andnonhalogenated yttrium acetates.
 45. A composition, comprising: a saltof a rare earth metal; a salt of an alkaline earth metal; and acarboxylate salt of copper.
 46. The composition of claim 45, wherein thealkaline earth metal salt comprises barium trifluoroacetate.
 47. Thecomposition of claim 46, wherein the rare earth metal salt comprises asalt selected from the group consisting of halogenated yttrium acetatesand nonhalogenated yttrium acetates.
 48. The composition of claim 45,further comprising a Lewis base.
 49. The composition of claim 48,wherein the alkaline earth metal salt comprises barium trifluoroacetate.50. The composition of claim 49, wherein the rare earth metal saltcomprises a salt selected from the group consisting of halogenatedyttrium acetates and nonhalogenated yttrium acetates.
 51. A method,comprising: disposing a precursor solution onto a surface of a layer toform a precursor film, the precursor film including a salt of a rareearth metal, a salt of an alkaline earth metal, a salt of a transitionmetal and a Lewis base; and treating the precursor film to form anintermediate of a rare earth metal-alkaline earth metal-transition metaloxide.
 52. The method of claim 51, wherein the Lewis base comprises anitrogen-containing compound.
 53. The method of claim 52, wherein thenitrogen-containing compound is selected from the group consisting ofammonia and amines.
 54. The method of claim 52, wherein thenitrogen-containing compound comprises an amine having a formulaselected from the group consisting of CH₃CN, C₅H₅N and R₁R₂R₃N, whereineach of R₁R₂ and R₃ are independently selected from the group consistingof H, a straight chained alkyl group, a branched alkyl group, analiphatic alkyl group, a non-aliphatic alkyl group and a substitutedalkyl group.
 55. The method of claim 51, wherein the layer of theintermediate has a surface adjacent the surface of the first layer andthe layer of the intermediate has a plurality of volume elements, andwherein defects contained within the intermediate comprise less thanabout 20 percent of any volume element of the intermediate defined by aprojection of one square centimeter of the surface of the intermediate,and the intermediate is free of any defect having a maximum dimensiongreater than about 200 micrometers.
 56. The method of claim 51, whereinthe precursor film is treated for less than about five hours.
 57. Themethod of claim 51, wherein the layer of the intermediate has a surfaceadjacent the surface of the first layer and the layer of theintermediate has a plurality of volume elements, and wherein defectscontained within the intermediate comprise less than about 10 percent ofany volume element of the intermediate defined by a projection of onesquare centimeter of the surface of the intermediate, and theintermediate is free of any defect having a maximum dimension greaterthan about 200 micrometers.
 58. The method of claim 51, wherein theintermediate is capable of being processed to provide a superconductormaterial having a critical current density of at least about 0.5×10⁶Amperes per square centimeter.
 59. A composition, comprising: a Lewisbase; a salt of a rare earth metal; a salt of an alkaline earth metal;and a salt of a transition metal.
 60. The composition of claim 59,wherein the Lewis base comprises a nitrogen-containing compound.
 61. Thecomposition of claim 60, wherein the nitrogen-containing compound isselected from the group consisting of ammonia and amines.
 62. Thecomposition of claim 60, wherein the nitrogen-containing compoundcomprises an amine having a formula selected from the group consistingof CH₃CN, C₅H₅N and R₁R₂R₃N, wherein each of R₁, R₂ and R₃ areindependently selected from the group consisting of H, a straightchained alkyl group, a branched alkyl group, an aliphatic alkyl group, anon-aliphatic alkyl group and a substituted alkyl group.
 63. Thecomposition of claim 59, wherein the transition metal salt has a formulaselected from the group consisting of M

(CXX

X

—CO(CH)_(a)CO—CX

X

X

)(CX

X

X

—CO(CH)_(b)CO—CX

X

X

), M

(O₂C—(CH₂)_(n)—CXX

X

)(O₂C—(CH₂)_(m)—CX

X

X

) and M

(OR)₂, wherein M

is the transition metal, a is an integer having a value of at least oneand at most five, b is an integer having a value of at least one and atmost five, n is an integer having a value of at least one and at mostten, m is an integer having a value of at least one and at most ten, Ris a halogenated or nonhalogenated carbon containing group, and each ofX, X

, X

, X

, X

, X

, X

, X

, X

, X

, X

, X

is H, F, Cl, Br or I, with the proviso that the transition metal saltdoes not have the formula M

(CF₃CO₂)₂.
 64. The composition of claim 59, wherein the transition metalsalt comprises a carboxylate salt.
 65. The composition of claim 59,wherein the transition metal salt comprises Cu(C)₂CC₂H₅)₂.
 66. Themethod of claim 1, wherein the layer of the intermediate has a surfaceadjacent the surface of the first layer and the layer of theintermediate has a plurality of volume elements, and wherein defectscontained within the intermediate comprise less than about 20 percent ofany volume element of the intermediate defined by a projection of onesquare centimeter of the surface of the intermediate, and theintermediate is free of any defect having a maximum dimension greaterthan about 200 micrometers.
 67. The method of claim 15, wherein thelayer of the intermediate has a surface adjacent the surface of thefirst layer and the layer of the intermediate has a plurality of volumeelements, and wherein defects contained within the intermediate compriseless than about 20 percent of any volume element of the intermediatedefined by a projection of one square centimeter of the surface of theintermediate, and the intermediate is free of any defect having amaximum dimension greater than about 200 micrometers.
 68. The method ofclaim 67, wherein the intermediate is capable of being processed to forma superconductor material having a critical current density of at leastabout 0.5×10⁶ Amperes per square centimeter.
 69. A method, comprising:disposing a precursor solution onto a surface of a layer to form aprecursor film; and treating the precursor film to form a superconductormaterial having a critical current of at least about 200 Amperes percentimeter of width.
 70. The method of claim 69, wherein thesuperconductor material has a critical current of at least about 300Amperes per centimeter of width.
 71. The method of claim 69, wherein thesuperconductor material has a critical current of at least about 300Amperes per centimeter of width.
 72. The method of claim 69, wherein theprecursor solution comprises a salt of a rare earth metal, a salt of analkaline earth metal and a salt of a transition metal.
 73. The method ofclaim 72, wherein the rare earth metal is yttrium, the alkaline earthmetal is barium, and the transition metal is copper.
 74. The method ofclaim 69, wherein the superconductor material comprises a rare earthmetal-alkaline earth metal-transition metal oxide.
 75. The method ofclaim 69, wherein the superconductor material comprises YBCO.
 76. Themethod claim 69, wherein the method includes forming an intermediate ofthe superconductor material.
 77. The method of claim 76, wherein theintermediate is metal oxyfluoride intermediate.
 78. The method of claim1, wherein the intermediate of the rare earth metal-alkaline earthmetal-transition metal is further treated to form a superconductormaterial has a critical current of at least about 200 Amperes percentimeter width.
 79. The method of claim 15, wherein the intermediateof the rare earth metal-alkaline earth metal-transition metal is furthertreated to form a superconductor material has a critical current of atleast about 200 Amperes per centimeter width.
 80. The method of claim32, wherein the intermediate of the rare earth metal-alkaline earthmetal-transition metal is further treated to form a superconductormaterial has a critical current of at least about 200 Amperes percentimeter width.
 81. The method of claim 51, wherein the intermediateof the rare earth metal-alkaline earth metal-transition metal is furthertreated to form a superconductor material has a critical current of atleast about 200 Amperes per centimeter width.
 82. The method of claim 1,wherein the carboxylate salt of the transition metal comprises apropionate salt of the transition metal.
 83. The method of claim 15,wherein the carboxylate salt of the transition metal comprises apropionate salt of the transition metal.
 84. The method of claim 32,wherein the carboxylate salt of the transition metal comprises apropionate salt of the transition metal.
 85. The composition of claim45, wherein the carboxylate salt of copper comprises a propionate saltof copper.
 86. The method of claim 51, wherein the salt of thetransition metal comprises a carboxylate salt of the transition metal.87. The composition of claim 59, wherein the salt of the transitionmetal comprises a carboxylate salt of the transition metal.
 88. Thecomposition of claim 69, wherein the precursor solution comprises aLewis base.